I did the same for 10U Rec last year, had 3 kinds of stickers for offense, defense, game changer (kind of like MVP). Worked great, no complaints. We tried to spread it out but I think 4th and 5th graders are also old enough to understand the not every kid is the star and not everyone contributes the same amount every game. Probably didn't hurt that we only lost one game all year, people don't gripe about much when you win.