OK,...let's rephrase this question...My son has had a couple of fizzy/foamy poops.?

this q and your last q struck me as odd. sorry. i don't know about a 5yr old's poop, but i know when my girls were a few months old and i had too much dairy, their poop was frothy/foamy (they breastfeed and are dairy sensitive)

could he have a food sensitivity that y'all hadn't realized before?

(i've been dairy sensitive all my life and didn't realize it until i had to keep a food journal to track my diet as well as my dd1's diet...so i was 23, when i realized *i* am dairy sensitive)

otherwise, i don't know what could cause "fizzy poop"

EDIT: one of the signs of a food sensitivity is self-limiting to that food. (i.e. - i am dairy sensitive. but ALL of my favorite foods are dairy. if it's in the house, i have very little self-control and end up eating the whole container without realizing it. then i may or may not have mild cramping - not enough to complain about. what changed my eating habits, was my daughters being in pain from me eating such things [too much dairy would get into my breastmilk])

another sign of a food sensitivity is complete disgust of a food. it's odd i know, that 2 opposite, seemingly unrelated symptoms can be the signs of the same thing. but it has to do with the way your body reacts to the food. extreme like/dislike of a food could mean some kind of imbalance.

It is not likely. Pee actually has a small amount of ammonia in it - and when they're both present in the bowl at the same time, fizzing generally does not occur. So no, ammonia is unlikely to react with anything in poop to make a fizzy/foamy reaction.

Plus, unless you had not flushed the toilet since you cleaned it, the amount of residual ammonia would be no more than is in normal urine anyway.

Maybe you should call the doc, and take them a stool sample.

or Maybe your son put some alka selser in the toilet when he pooed.

I don't really know, but i'm quite sure your son isn't pooping foam