I don't have any trouble with any of the inexpensive shorts that have a flat pad, like this:
which is the inexpensive Performance Classic.
I don't like the sculpted ones like this:
If you can get the kids to accept saturating the pad with a load of vaseline before wearing ("Ewww, that's gross!"), there shouldn't be any saddle sores, partly because of the lubricating effect and partly because the bacteria can't multiply in it. Putting more vaseline in before each wearing, without washing, makes you get the maximum protection after 3-4 days, and that protection continues many, many rides after that. After each ride, set the shorts out, inside-out, pad up, exposed to the air, until the next ride. I know it's very unconventional, but it works the best of anything I've tried.
In any case, they should not wear underwear under the cycling shorts.