If the child has acne they could use concealer or foundation. If a child wants to experiment then sure why not, but if it's inappropriate then teach them proper tequnice. Get shuttle colors and not bright and powerful and always look your age. Just be yourself and enjoy your life
WhY putting babies in makeup they grow up to fast and their skin is beautiful, soft and gentle! They don't need to hide anything! Youthful and perfect! Leave them be and left them be kids while they can! They are beautiful in their own right! No need to improve anything!