I live in a 2 bed home, with 6 of us, so no, you are not a bad Mum for having a roof over your childs head!
We can't afford to move, we have been on the waiting list for 11 years for a larger home, however, I won't push it the way folk tell me to, as I made my bed lol, so I shall lie in it, even though, I don't actually have a bed, I have a sofa in the front room that I share with the husband, man its hot in the Summer lol.
Luckily I had two of each, and the two boys share their tiny room, as do the girls, they have bunk beds and a telly, not much room for much else and there isn't enough room to swing a cat (not that you'd want to, poor puss!)
But, our lack of space has actually made the kids want to do well, as all of them tell me how they are going to get amazing jobs just so they can buy Mummy & Daddy a bedroom bless 'em....sounds good to me!
They are growing, thriving, working hard, happy, playing, and yes, while they don't have much space, Ive still kept them off the streets and in a warm comfy bed, so don't beat yourself up! :-)