We've done it a few times, so have others on mumsnet, it's always been very successful. In fact we find it more relaxing than a hotel or B&B with 3 small children - it's less fussy, less to break, less to spill, less anxiety about noise and children racing around the place like mad things.
You can come back to your room at any time once you've booked in. We usually have ensuite bathrooms, otherwise there will be male and female showers separately, the loos might be single ones, unisex. Not grouped together unisex, or not that I've come across.
They vary in spartan-ness and whether they have wardrobes or lockers in the room, some have been done up lately and they are much smarter than the older ones.
Food in box in communal kitchen. Very handy with small children.
Really, it's great. Very child friendly, especially the communal living rooms and tv rooms and dining rooms and, often, large gardens.