SUBREDDIT: r/AskDocs
TITLE: 5yo boy suffers from massive b.m. that clog toilet every time
POST: My brother is 5. Today he used the bathroom, clogged the toilet, it overflowed. He tried to use a plunger himself but only made more of a mess. He was embarrassed and didn't tell his mother and so she had a nice surprise. I remember changing him when he was in diapers, and he would frequently have baseball sized (and shaped) poops that were as hard as a rock. Flushing them would clog the toilet even then. I am posting this on behalf of my mother who wouldn't have any idea how to do this. 

He refuses to eat anything besides meat and potatoes (if that) and occasionally some fruit. The best solution I can think of is to either MAKE him eat other foods too (I don't know if his mom has the strength to force him to do anything), or to give him some sort of fiber supplement. Maybe both. Is it safe for a 5 year old to take fiber pills? Is there some other solution we can't come up with?
TL;DR: 
my brother (5) has had hard, toilet clogging bowel movements his entire life. How can we alter the size and toughness of his poop?