“What can you give a child for constipation?”

Increase fluids and fiber in the diet. You can use something like Miralax over the counter.

It depends on the age of the patient and the cause of constipation. If your child is an infant make sure she is drinking plenty of fluids and if she is over 4 months she can have 2 ounces of prune juice for mild constipation. If your child is over one year old and has occasional constipation then 4 ounces of prune juice may help. If your child has chronic constipation the best treatment is Miralax. Consult your pediatrician if constipation continues

This is more a question for a pediatric GI doctor. I only treat adults. But it depends on the age of the child and how severe the constipation is.
Typical treatments might be glycerine suppositories, Miralax, fiber.