I don't know because I'm not a parent yet, but I don't think this should happen..?

Question

I was with my friend and her kids for about 1 hour going to the out of state beach. We were stuck in traffic and one of her children (3 years old) had to pee. He has been potty trained for 3 months. She didn't want to stop, so he goes in the backseat (I'm driving) puts a diaper on him, and tells him to go in that. Won't that be incouraging him to pee in a diaper again?

Answer 1

Probably not.  At that age, it's really hard for them to hold it for long periods - it can even be damaging.

What was the alternative?  Letting him wet himself/the car?

And to be honest, there's always a chance they will regress, even without something like this happening.  

Sometimes, parents have to make the best decision they can.  It's not always the best and sometimes it's tackier than all get-out...LOL!

Answer 2

Children rarely regress to that extreme.  You should encourage your friend to keep a potty seat or portable potty for such journeys or be prepared to stop when ever the little one has to go.

Having him "go" in a diaper once to get him comfortable, was a better option than having him wet himself in his big boy underwear.