We kept our 4 week kittens we were fostering in the spare bathroom. Kept the toilet lid closed and the tub closed. Once they could jump and climb more we had their litter box in the tub over a towel on the drain(to make sure they didn't get caught) to give them more room to run around and jump. Once they grew out of the bathroom we gave them a spare bedroom to live in. We also would let them run around the house (with some doors closed off) under our supervision a few times a day so they could get plenty of play time and exercise!
If you can't kitten-proof any room besides the bathroom, maybe just make sure you allow them to roam some bigger rooms a few times a day under your supervision...that way you can make sure they aren't getting into anything bad. Also in a small place like a bathroom, you can make things for them to play on...we taped up a box and cut some holes in it so they could play, climb, hide, pounce from the holes and sleep inside or on top of it.
Good luck with them, this is a FUN age! Can't wait til our 10 day old kitties start playing!