the more sugar the better. ABC has always been a favorite. Also, kids are messy and the ABC crusts so it doesn't soak into clothes and stay on fingers as long. A kid with a handful of silky, buttery SMBC can do a lot of damage.
I have made IMBC and iced cupcakes with it before and my when my Niece at it she had a reaction to the egg whites in it. If it was for children and you do not know what allergies they have etc I would stick to normal buttercream as it does not have raw egg whites in it.