I've heard anecdotally that some mothers will list the dates of birth of their children on their CV, but I've never seen it done myself. The intended effect seems to provide a kind of excuse for lower output around those dates, I suppose. Is this common? Am I totally misinterpreting the motive?
This is common in Europe. Parents are not supposed to (and to some extent not allowed to) work during maternity or paternity leave. Thus, such periods are deducted from your phd-age, tenure clock etc.
Quoting from the ERC Starting Grant 2017 call:
For maternity, the effective elapsed time since the award of the first PhD will be considered reduced by 18 months or if longer by the documented amount of leave actually taken for each child born before or after the PhD award. For paternity, the effective elapsed time since the award of the first PhD will be considered reduced by the documented amount of paternity leave actually taken for each child born before or after the PhD award.
And from one of the largest commercial foundations supporting basic research in Denmark, which explicitly states that the CV should contain this information:
In the case of maternity leave, the number of months on leave, times two, will be deducted from the seniority. The specific dates for the period of maternity leave must be clearly stated in the CV/resume.
Well, I uncovered a few via Google search, so they definitely exist. It seems to be more of a European thing - which is probably because maternity/paternity leave here is often more generous than, say, the States - so taking your six month entitlement will result in a more noticeable gap in your CV. I wouldn't describe it as an 'excuse for lower output' though - more an explanation of what would otherwise be a gap in the CV. Also, it should be noted that it is not limited to mothers.
If you conduct a search on a term such as 'academic cv "child born"' you will find a number of examples of male and female academics who provide the dates of birth of their children in their CV.
An alternative that I've seen (though not often) and which feels a bit less weird to my American eyes, is to list the time of parental leave under the employment section. These are the two examples I remember, and which made a positive impression on me as handling this point very nicely. Including the details of employment status (change of title, travel leave, parental leave) seems clearly relevant to me, while listing birthdays of children feels like it's mentioning things I'm not supposed to be considering during hiring (family status) and comes off as strangely European in the same way as putting a photo or your age on a CV.
Australian perspective: There are many situations in academia where family commitments would be taken into consideration when evaluating academic output. A few obvious contexts include: grant applications, job applications, and promotion applications.
Grants: As with the European example, most Australian early- and mid-career grants which are defined in terms of years post-PhD allow for that date to be extended based on parenting commitments.
For example (quotes thanks to @Joel), the ARC (the main government grant giving body in Australia for non-health related grants) state that:
"Periods of unemployment, or any career interruptions for child birth, carers’ responsibilities, misadventure, or debilitating illness will be taken into account." - source
Or for this year's DECRA grants (i.e., a major early career grant in Australia):
"A DECRA Candidate must at the closing time of submission of Proposals: have been awarded a PhD on or after 1 March 2010 or ...The ARC may grant an Eligibility Exemption for the DECRA Candidate who has been awarded a PhD on or after 1 March 2006, together with periods of significant career interruption... The following types of interruption will be considered... maternity or parental leave..."
Employment: Many universities would have HR policies related to employment and promotion that look at what is sometimes called "achievement relative to opportunity". In such cases, time off due to parenting responsibilities reduces the "opportunity" part of the equation.
Legal/cultural context: More generally, Australia (as with many countries) has anti-discrimination legislation. This creates legal obligations, and it also forms part of a broader cultural initiative. Universities (who award jobs and promotions) and the government (who award the big grants) tend to be progressive on such matters. Anti-disrimination legislation include many categories, but of particular relevance here are parental status and sex (i.e., females are more likely to take leave and have more of the primary care responsibilities, especially in the months leading up to birth and the year or so post-birth).
Implications for CVs: I think it would be more common to have a couple of sentences explaining the timing of parental leave and noting that consequently academic output was reduced during that period. That way, the relevance between the birth dates and the CV is made more explicit.
Language and the word "excuse": Finally, I wanted to comment on your statement (my bolding):
The intended effect seems to provide a kind of excuse for lower output around those dates.
It is not meant to be an excuse. I think the word "excuse" implies that reduced output needs justifying. Rather, the legal context and the associated cultural change is trying to frame parenting commitments as fundamental to a functioning society. So instead, evaluating output relative to opportunity is framed as "the default". Therefore, for some people opportunity is indexed by time. But for people who have had major parental obligations, it is indexed differently to incorporate the time away due to parenting commitments. Perhaps, this is a subtle distinction, but I think it is important.
I was thinking that it was a shame that we hadn't had any comments from people who have included their child's name and birthdate in their CV, as it would be helpful to get their perspective in order to understand the 'motive' part of @pburg's question.
Today I came across this blog post written by Megan Rivers-Moore, Assistant Professor at Carleton University, Canada, who has included her children's names and birthdates in her tenure file (she doesn't specifically say CV). It's hard to distill the post down to a few words, but the gist seems to be that she considers her pregnancy and subsequent transition to parenthood important enough in her life to be relevant to those seeking to understand her as a professional.
While acknowledging that it is just one person's perspective, it is well worth a read, I think, as it gives some idea of her reasons for so doing.
Many European countries have strong law-bound parental leave benefits - also for the kids' fathers - it is likely there to provide explanation to future employers for past gaps of employment - or for parental leave.
And there is also a completely different mentality regarding these matters. Calling parenting an "excuse" for the presumed higher value of employment will definitely give some eyes on you so to speak.
Here in the US, unless you're a politician running for office, this is not common and it's hard to imagine a worse idea for a professional woman's CV. It needlessly invites male stereotyping of women as unreliable workers because they leave their careers to have children.
From 'Motherhood Penalty' Can Affect Women Who Never Even Have a Child, NBC News, April 11, 2016:
In a 2013 study, Mary Ann Mason, professor and co-director of the Center for Economics & Family Security at the University of California Berkeley School of Law, revealed some alarming outcomes for women in academia: Women graduate students who are pregnant or mothers with young children are 132 percent more likely to be working in a contingent position, while men with a young child are 36 percent less likely to be in a contingent position. Contingent positions are non-tenured, adjunct, or temporary jobs that are not secure. ...
"Pregnant women and mothers are assumed to be less committed to their careers, and every time they leave the office or ask for any flexibility, that commitment is further called into question," Slaughter said.
"This kind of discrimination is institutionalized," said Lisa Maatz, a policy adviser with the American Association of University Women. "It's a part of the culture, it's a part of the decision-making process. Right now the assumptions about women's roles, as stereotypical as they may be, are driving decisions and those decisions disadvantage women."
In an earlier comment since moved to chat, I was asked to consider a hypothetical case, that "a woman 5 years past PhD applying for an academic position who reports having 2 children would have her output judged as if she were 2 years post PhD", possibly allowing her to qualify for a grant with a time-since-PhD cutoff. But putting this on a CV also reminds readers that she still has two children under 5 who will be competing for her attention for at least the next 13 years. In a situation like this, I would try hard to disclose this information in some way other than my CV, e.g., an email, a cover letter or explanatory note on your application that puts them on notice why you're disclosing this information and isn't likely to be circulated as widely.
The best strategy for professional women is a CV that minimizes any personal information that isn't directly supportive of why you're the best for the job you want. If you have a break because you had kids, especially here in the US, make them ask. You will both recall the exact moment they received information they cannot consider in a hiring decision.
From Pre-Employment Inquiries and Marital Status or Number of Children, US Equal Employment Opportunity Commission:
The following pre-employment inquiries may be regarded as evidence of intent to discriminate when asked in the pre-employment context:
Whether applicant is pregnant.
Marital status of applicant or whether applicant plans to marry.
Number and age of children or future child bearing plans.
Child care arrangements.
Employment status of spouse.
Name of spouse.