There are many sixth grades that play football, but cannot be exactly counted due to the amount fo recreational, travel and school teams worldwide.
FOOTBALL (The one they actually play with feet ;)
In terms of Soccer (Football) there are over 2 million that play professionally on some level. It is estimated that 2.65 billion people play the game worldwide altogether.
About 30 million people play basketball worldwide
Not me, sooo...
Thousands of people play football, from all ages. Even girls play football.