How do I paint plastic?

I want to personalize some plastic boxes as party favors. What paint do I use? Any pens out there that will stay on the plastic and be safe for little ones? I am hoping to write names on the boxes and paint some designs.

Thanks :)

I don't know about the safety part, I do believe they say they are non-toxic (but who knows what that really says, if anything) but I have used sharpies on plastics and it holds up nicely and they offer a ton of colors. There are also paint pens, or just regular old acrylics if you have a steady hand to use a paintbrush. If the plastic would be washed, say if it's a cup or something similar I don't know if paint would hold up very long. Good luck with your party favors!!

HTH
Heather