Can Nido Formula Cause Constipation In A Toddler?

My grandson is drinking Nido for 1 to 3 years old formula. He s always constipated. We tried diluting it with water, but it takes him long to finish a bottle. He s not fond of eating rice and vegetables. He s a picky eater so that his parents are forced to give him Nido with dilution of 1:1. Glycerin has to be put on his anus just so he would move his bowels. And he cries a lot if this is done. Help!