You watch the kids behavior. Most kids being abused in any form including getting beaten are going to act out in their behavior. A person who knows what they are doing will get tons more useful information out of a kid talking to them first for a considerable time likely several times than jerking down their pants for a look in their privates.
Unless the perp is actually engaging in a full act you likely won't be able to determine anything in that manner. If a kid is showing bleeding in that area at school yea you have a problem Houston. Most sexual abuse in very young kids can not be detected by a physical exam. Most just touch the kids or have the kids touch them
These creeps are so careful they have the young kids look elsewhere so anatomy of the perp can not be described to authorities.
It's not hard to get kids to talk. Given the opportunity, kids will spill their guts to an adult they like and trust.
We lived in a rough neighborhood for some time and I always felt sorry for the neighbor kids and would try to be extra kind to them and give them snacks, like cookies and stuff when they were hungry. I never pried for information either, but they'd just start talking and telling me all kinds of things that I'd rather have not known. Nothing that would qualify as actual abuse to them by someone, but just family politics that leave you just shaking your head.
But they will tell all if you are willing to listen.
Not disputing anything you wrote, but the bottom line is that I don’t fault the nurse for doing the examination.
If she would have discovered and reported abuse, a lot of people here would be giving her kudos....especially on threads dealing with the perp.