Moisture, yeast and heat.
And darkness.
That's how they grow.
He had trouble urinating. He said it burned. The affected area was very red. It responded to a yeast-killing medication.
Just because you can't imagine it doesn't mean it didn't happen. There are lots of things you can't imagine.
I do know quite a bit about three-year-olds. They are just like other people. Some of them cry at the drop of a hat, and some of them take great provocation. This little fellow was one of the latter.