When I worked for the City of Ft.Collins I did a lot of work/play with 4-8 year olds while I was coaching hockey. When we'd check them in and they'd get their gear I always gave them a puck. I told them they could paint it or put stickers on it or whatever. It didn't matter. They had to throw their pucks on the ice the first time we practiced. They got mixed in with the regular pucks we used. But after practice all their pucks went in a separate bucket. At the end of the season we'd dump that bucket of pucks on the ice and shoot them all over the ice. Each kid got to grab one. We always made sure every kid got one. Then they'd go in the locker room and try to figure out who's puck they got. I had kids that had collected pucks from every season I coached them. 4 seasons a year. It was always cool seeing them in the locker room with those pucks. Hockey sticks,marbles and or painted rocks are not a good mix.