What are small white worm-like things on your child's anus?

they are worms. kids get them from putting their hands in their mouths after playing in the dirt or sand and eating the worm eggs, they get them from contact with other kids that have worms or if the worm eggs are on their food.

They are not dangerous, when the eggs hatch and they begin to mature the females will leave the body through the anus to lay eggs.