Both of my children - ages 12 and 14 - seem to have HUGE bowel movements. I only know this because they often forget to flush, or are afraid to flush knowing that the toilet will most certainly back up.
Please know that I am not exagerating, some BMs are as large as a man's closed fist. I have not ever seen anything like this in my various, and often disgusting, tours of the world's bathrooms.
What could this mean?
I once heard of a medical condition called "Wide Anus Syndrome." Basically, I guess, the hole down there is bigger than normal or something and causes large stool. It's something you might be able to perform an internet search on and find some more answers. Good luck!
Also could be they are just constipated, and the stool will build up to a large size, until it comes out. I'm sure you are familiar with how to ease constipation, but as a reminder, they should be getting plenty of exercise, drinking plenty of water, eating plenty of fiber type foods, to include things like cheerios and 100 percent whole wheat bread, and at their bathroom times they should not be rushed.
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