Lots of water first (but not too much) (no soft drinks or milk) and some fiber afer a few days if the water alone does not do it. Just take your time, i assume your child is not feeling bad, any pain etc....
Try the product "Experience" from the link below. Make a tea and sip at night before bed. It is very powerfull so start out by using 1/4 of a pill in a tea for 4 days, then up it to 1/2 for 4 days to see if it is working on a nine year old.