Is it possible to work and save childs in the repository?

Question

PHP

I want to make a repository that will work internally with an external service and with an internal database. Everything should be transparent to its users. I can not decide how to work with child objects. On the one hand, I want to have a transaction inside update where everything will be saved. On the other hand, it may be worth moving the work of child objects to other repositories. And the question arises again: is it possible then to work with child repositories in the main, or is it necessary to separately transfer and save data from the call site first for the main object, and then for the child ones? In this case it is necessary to do transaction too "outside".
How to do?