Nothing sells a house like a kid stripping in the middle of a mess.
Wouldn't it be nice to tell your kid to "go play doctor" and he'd step into his own little TARDIS and go on an adventure while you take a nap and drink some wine? I don't even have kids and this sounds pretty great.
A super fort, super bunker, super bed, super hideout and super play structure. This kid is gonna turn out awesome. BAM!