Well there are two sides to this. Parents allow their kids to play sports in the heat, and coaches push their kids too hard. If you want to keep your kids safe do not encourage them to play sports in the excessive heat, but some might think I am too protective.
I am not taking sides, I am just saying some people are more heat sensitive than others. I can handle hundred degree plus weather, but many people I know swelter just walking from their car in this type of heat. However, to be on the safe side it might be a good idea not to let your kids play sports in the heat, and several kids have died here in Southern California from the same type of thing.