Twenty six years ago my son had to do a family history research project for school. Admittedly he was 15 at the time......but I am so glad he had this task. It meant lots of time as a family finding out things, talking to grandparents, visiting libraries and records offices, going to places where the first emigrants lived. There was no emphasis on things like certificates at all .....more on the social history side of it, though he was expected to draw up a family tree. He did this on a huge roll of paper, and I still have it.
When completed, it was all put away in a cupboard and forgotten..... until I retired and was looking for a mentally stimulating hobby.

Oh....how the tree has grown now, and now certificates have become an important part of it.
As a former teacher of young children, we often did a unit of family history, but the emphasis was not on absolute proof or providing photographs. It was on the idea of a much greater family than just Mum and or Dad and/or siblings, plus of course social history such as comparing what it was like when Mum and Dad grew up, or grandparents grew up. And it always was handled with consideration for the circumstances of different children and families.
You'd be amazed at how many young children know they have grandparents, but don't realise that their parents have parents.....and these are who their grandparents are.

I firmly believe that a family history study can teach about relationships in a broad sense, not just a blood family sense, as well as begin an understanding of history. But it should always be handled in a sensitive manner.
.....dee