If the issue is not much separate quarters but comfortable berths, would it be crazy to use a quarter berth for one child and one of the settee that is opposite the dinette set +seats as the dedicated berth for second child? Or is that settee best reserved as an sea berth for use while underway?
Bunks sound like an excellent idea as well. Most boats don't seem to come equipped with them, but I suppose they could be installed in any location that had sufficient headroom.
Quarter berths are great kid zones, as indicated by kd3. Some boats have them P&S. The challenge is then where to put all the gear that most boaters cram back there!
Settees will work but of course you're in the middle of things. Using a settee as a kids berth when in port doesn't preclude using it as a sea berth when underway. Kids can probably sleep anywhere.
The pipe berths worked well for us, the ability to level them was handy underway, and the kids loved the rigging and that they could 'close' themselves up in them. But unless you're prepared to buy an older relatively spartan race boat you're unlikely to get them. On the flip side if you are willing to do so you'll tend to get more boat, better performance and better gear (though less comfort and fewer amenities) for your money.
For younger kids, ideally a separate aft cabin with two bunks would be great. However, if the kids are teens the ideal arrangement is to simply tow them in the dinghy. There is only room on a boat for one person who thinks they know everything, and that person is me.
LOL.... why didn't we think of that?
(would have needed a bigger dinghy!)