As a general rule, make-up is not for kids. However, there are times when they are required to have some color on their faces when the occasion calls for it. For instance, if the kid is going to be performing on stage, then she will need a little color so that she will not appear deathly up there. Make-up for kids is done on necessity, and that is, to add or give color to the face for stage presentations.
However, there had been many cases of kids being made up a la Marilyn Monroe especially during kids' pageants. Ok, ok. It's a beauty pageant, but these are only kids! For God's sake, shaving their eyebrows and making them arched will turn them into hags!
Kids, no matter what presentation they are joining, should look their age. A small amount of blusher and a dab of lipstick will do just for the color effect.
Otherwise, please, do not tamper on their innocent faces.