Intussusception is a part of intestine moving into another in your child's case you said it was small intestine moving into colon and fortunately it could be reduced by gas treatment – which is good – correct thing to do. You have to be cautious in future. There is no definite reason in most why it happens. It may/may not recur again. In case of pain abdomen, excessive crying of child, passing of blood in stool, please contact a doctor immediately.