People throw around the term soundproofing, but likely they'll put up something like this:I also see why Tim is obsessing over getting sound proofing in the rooms, but I would never want to drown my kid out though.
Which is really to control reflections and absorb some high end. But, if they really want to soundproof, they need to build a decoupled room within a room. Put a layer of heavy neoprene all around, then build the room inside that and make it solid, don't screw it to the outside walls. Also, ideally you have two doors with rubber seals all around and about a foot in between to air gap it.
Or, there are also tracks you can hang over the drywall to hang a new layer of drywall, again giving it an air gap. That's way more expensive and definitely the way to go if you really want soundproofing.