gel for a 9 year old? i would definitely not suggest so dear.
your baby is too young to try using a gel, even if it is for a one time event or occasion. these products contain a huge amount of chemicals, and you will end up putting this on your baby's very sensitive scalp. not to forget taht your baby will eventually touch the hair and scalp and may put the finger in his mouth or even in his eyes, all of which can be harmful. please avoid using a hair gel or any such chemical based product for your baby as much as you can.