Thank you for your query,
Inspite of taking fruits, whole grains and vegetables, your child is having constipation
Because of constipation gases will form in colon and it will lead to wind.
You can give oral stool softeners like lactulose syrup in prescribed dosage.
Constipation in your child should be evaluated by doing ultrasound
abdomen to rule out any structural anomalies of the large colon like Hirschprung disease and blood investigation to rule out hypothyroidism
So consult your Pediatrician
for further evaluation of constipation in your child.
Hope i have answered your query.