During my PhD thesis, I supervised the creation of Bachelor's and Master's theses. The official supervisor was always my own PhD supervisor (since I am officially not yet allowed to do university-level teaching on my own), but in practice I did almost all of the supervision. Topic and technical approach were usually my ideas (and related to my own thesis topic) and I coached students closely during implementation, analysis and writing. These were research-level theses, so the students simply lacked prior knowledge and experience to come up with really useful conceptual contributions.
I am now in the process of writing up my own thesis. What is the correct way to incorporate these results - which have already been written about in student theses but not yet published - in my own thesis? Essentially, all of the relevant technical details were proposed by me, so I really don't feel like it would be fraudulent to include these in my thesis. However, I must, of course, give credit to the students. Would it be fine if I simply add an acknowledgement in the corresponding section of my thesis and cite the student's thesis? I for sure don't want to be accused of plagiarism in the future for doing this.
I'm in an engineering field at a German university, if that matters.