A child's digestive system is the same length as an adults but as a kid the digestive system is not stretched out as much but it will stretch out and seem longer the older the kid gets and as they grow.
The intestines that is a child's digestive system is about 1½ to 2 inches in diameter and about 10 to 15 feet inside a child depending on the size and age of the child.
As the child grows into an adult the intestine will stretch out to around 20 feet long but in reality the intestine is actually the same length.
But it's just squished in the child's body and stretches out as we grow.
Just like our skin is squished up and then stretches out as we grow as around our wrists when we are toddlers we can see the skin bunched up which allows enough room for the skin to stretch out and grow along with our bodies.