My son had surgery for hirschsprung after birth, he's 4 now and having trouble control his bowel movement when passing wind. Is this normal?

Always possible. Hirschsprung can be short and long segment. If a large amount of colin had to be removed then it may be hard for your son to control gas and solids or semi formed stool. You may need to contact his surgeon and peds gi. A plan of action to help make stool more solid could help. 4year olds often have bowel control problems do it may be normal.