They should because kids need a break other wise there brain will start to shut down and that is when you sleep and if you do get enough sleep it will show on your report cards that you failed your math test you will also fall asleep in school which is also not good
Everybody should be able to do what they want. People know their limits and what they are or not capable of. Children should be able to do what they want, I'm a child myself and I adore playing soccer. Soccer is my favorite sport and yeah sure I'll get hurt but guess what? I don't care. I can always use a bandaid to cover it up. So who cares if you get hurt? If its something you enjoy do it, Don't put a limit to it.
If kids are old enough to play tough sports they should also be responsible enough to know when enough is enough. Parents should also moniter their kids to make sure that they don't over exasut themselves. It is not the goverments job to tell kids how much activity they can have in the form of sports.