how to keep a 3 year olds bowel movement going?

So my 3yr old doesn’t like to deficate but also he has chronic constipation so I’ve changed his diet to fiber n whole grain also gotten lactose milk n karo syrup n pineapple juice n prune juice vege n fruits

Soak one dry fig in milk or water overnight and give him next morning. Constipation will disappear in a few days.