Tell a child to stop touching things and see how many things they touch, where they put their fingers, how many times they pick their nose etc and then you'll know.
My friend was in an airport recently. A mother dutifully used hand sanitizer on her 3 year old's hands. Within one minute the child had put their hands on every surface within a meter: arm rests, seat cushions, under the seat where the boogers and gum are, the floor, etc.
It'll only take a few minutes.