I'd go against mindstorms, that is way to advanced for a 4yo. If you want to go lego, Boost or WeDo is better :-) I especially went with Boost because I rememb

I'd go against mindstorms, that is way to advanced for a 4yo. If you want to go lego, Boost or WeDo is better :-) I especially went with Boost because I remember debugging minstorms at school and I really didn't want to interupt our play-time with a debugging session :D