( i’ve moved this to projects so you can get individualized responses based on your own household’s requirements, and because there tends to be a lot of brainstorming in threads like this. 
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As you’ll find from some of my comments in other similar topics in the forums, I am not a big fan of inactivity turning off lights. Particularly in the bathroom, for all the reasons that you gave. But There are a couple of different approaches you can try.
If, and this can be a big if, everyone in your household closes the door when they go in the bathroom, then you can wait to start the inactivity timer until the door opens again. That will be easiest to do with core. But it gets really tricky if the kids are small and you have a parent who comes in and out, or if there’s anyone who doesn’t close the door all the way.
In the past, people have tossed a humidity sensor into the mix, basically automatically adding more time if the humidity goes up. That’s to account for people in the shower or the tub where they may not be detected by a motion sensor.
You can find some additional project reports by using the quick browse lists the community – created wiki, look in the project report section by room, and check the bathroom projects list.
Another option which might work better for the situation where parents might be coming in and out of the bathroom, or where you have two kids sharing a bathroom, would be to use a couple of motion sensors defined as a zone, one in the hallway just outside the bathroom, one in the main part of the bathroom, and if doable, one in the bathtub area. And delay the inactivity timer until there was no motion in all three of those areas.
Alternatively, as you mentioned, just bump up the inactivity timer to 45 minutes. That way the lights don’t get left on all night, but you’re not likely to turn them off when someone is still there.
This is just one of those situations were different solutions will work for different households, because it depends very much on what your own family’s usage patterns are.