Ours our a bit younger - 6 year old twins. We are only giving them $25 for the entire trip. We are on the DxDP so they don't need it for snacks or anything only for souvenirs.
Last December we went over board with giving the kids money for souviners, so this May trip we are also giving them 25 Disney dollars or gift card instead fir their extras (tshirts, toys, etc.). We pay for the snacks and food items so that doesn't come out of their spending money
I don't think that is too unreasonable for younger kids. Now older ones can use their own allowance money etc for souvies as well as the money the parents allow them. I read on one of the threads once that someone gave Disney dollars as allowance money leading up to their trip...a great idea!