Laps are great for lots of things, but writing and drawing are not among them. Keep art projects from collapsing all over your child by making a custom-fitted travel desk out of a sturdy cardboard box. First, while she is seated, measure the height and width of her lap. Now, cut a half-moon big enough to comfortably fit over her legs on two opposite sides of the box and remove the bottom flaps.
If you have time, you can paint the box to dress it up and staple or glue smaller accessory boxes or envelopes to the sides for storage. You can also flip it over to store paper and other travel games inside when it's not in use.