Hi and Welcome to HCM,
What is the exact age of your child?. There is at most possibility of colonic polyp. Differential diagnosis is intussusception
. Intussusception is a medical condition in which part of intestine invaginated into another section of intestine. Constiptation may occurs in both conditions.
Don't worry it will be well visualized in colonoscopy
. If polyps there it can be removed during colonoscopy. Diagnostic and therapeutic treatment for intussusception is Barium enema
. Nothing to worry it can be well treated.
Wish you a speedy recovery.