Don't let those grey walls fool you! It's very easy to have a warm and inviting room with grey walls. Just make sure you have lots of organic, natural touches in the room, and lots of texture in warm creams and golds. I agree that a patterned is your best choice with young children. Also, don't spend too much in the rug because, even with the pattern to hide spills, it won't look nice forever. For sofas, I highly recommend slipcovered. They are completely washable and offer that cozy look you are concerned about. They are very much on trend these days. So, here's a bunch of pics for inspiration. Let me know if you are interested in sourcing any of these pieces out. They're mostly from Crate and Barrel, Pottery Barn, Pier One, etc.