Well there is probably nothing wrong with gatorade even though my father calls it gay juice. I cant see any reason why not. Im not a nutrionist though.

I think it is marketed to children somewhat i mean they use their sports heroes to advertise.
But i would recommend milk, water, and juice it definetly is better than gatorade and your kids probably just like it cause it makes them feel their cool i mean its really just flavored water with extra electrolytes (all they do is replenish salt so nothing wrong there)