Paint for kids' skin: what is suitable?
You can buy non-toxic "face paints" or "body paints" specifically made for this purpose. 

Product Search: Face Paint

You can also make them yourself.

Face paints (typically) are not a "type of paint" per se, but a mixture of food coloring or other non-toxic dye mixed with a base material to give it opacity. A lot of costume makers, face and body painters mix this up on their own with a combination of


Food coloring or non-toxic dye (for color)
Clay, corn starch, or arrowroot (for thickness and opacity)
Face lotion, vegetable oil or shortening, or zinc cream (diaper cream)


There are many recipes for face paint on the Internet based on what ingredients you have on hand and how effective/durable you need it to be, but I hesitate to list one here for having not tried any of them myself.

Search: DIY or Homemade Face Paint