I think reward and praise for participation is good up until about age 8-10. At that point, kids themselves become competative. When I played floor hockey in elementary, we were given specific instructions to play for fun. What did we do? We kept score. Even up until my parents stopped watching games, I was way more interested in answering "did you do well" more than "did you have fun".
Up until the approximate age where kids themselves stop caring about it, I think it's fine. Past that, it gets silly.
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