My guess would be:
44 inches long,
1 - 1 1/4 inches wide,
bendy handle,
leave the tips blocky but rounded,
12 pounds at full draw.
You’ll want something tough enough to withstand some abuse but not so overbuilt that the bows become dogs. Nothing more disappointing than a bow that doesn’t have any zip, especially for a kid.
Also, JW, you can’t give them something like a 55 inch bow. I don’t think 4-6 year olds get that tall. It might not be usable for them
Knowing my cousins, they’ll probably use them as half bow, half walking stick. That’s why the tips need to have some meat on them.