If kids want to dye their hair, let them. They have a freedom of choise and they should learn that they are allowed to look the way they want, and they have a right to be who they want to be. So if a child wants to dye their hair, let them however it should never be forced upon them.
It is not good because it can damage the hair badly and change the natural hair color it also doesn't promote self love and if the school catches you might be disqualified from certain things like school president or some other special programs most of all they are to young to put such strong chemicals on the hair.
Because hair dye can cause serious problems. Like diseases, skin problems, hair problems and allergies. Hair coloring can also make kids not appreciate their true looks. Hair coloring can also be disturbing in class and distract other classmates. That's why I think hair coloring should not be allowed for kids under age 7.