How many parents do you know actually watch their kid every hour of the day? Some parents actually have a thing called work that they have to do to earn money and in some cases that work involves more work while their at home.
You don't know for a fact that every child has learned that. Normally they wouldn't touch fire because the heat would tell them not to, instinct kicks in there. But if they believe some spell is going to keep it from hurting they might try it and if they happen to have a certain nerve-problem they won't feel it. That nerve-problem won't keep them alive though.
You have your opinion and I have mine. Your's seems to be to have fun with fire regardless of risk, that's fine. Mine is to be safe about it and not encourage kids who don't understand all the risks, such as burning the house down or a friend. The kid may not burn themselves, but if they think some chant is going to keep their friend from burning their are kids who would try it on their friend first.