It hurts when I Poop... Constipation has lots of consequences besides pain in passing stools.
Children may present with either of these:
1. Recurrent Vomitings
2. Pain in abdomen 
3. Loss of appetite 
4. Abdominal Mass
5. Fecoliths causing intestinal obstruction
6. Bleeding while passing stool
7. Spurious Diarrhea
8. Behavioural issues
9. Soiling - Most disturbing to self esteem.
10. Lots of school problems
So please do not take constipation lightly, else it'll become chronic. A stitch in time saves nine