As of several years ago, Pop Warner Football sponsors a tackle division for five- and six-year-olds. I have a hard time understanding why.
Five-year-olds are not demanding tackle football. The five-year-olds I know demand 10 more minutes at the playground or chocolate milk with their peanut butter sandwich, not tackle football.
For those kids who are charged up about the sport, there's always flag football. Kids run around just as much and it's far less violent. Why put a helmet on these kids and tell them to run over each other?