This sort of behaviour is quite normal. If the kitten is off the street and hasn't had a very good start to life, then he will need lots of patience. He will probably be quite scared at the moment, and there will be a lot of things for him to get used to: the new people, the new house, and all the new smells. Do try to encourage him to come out and give him lots of strokes and cuddles when he'll let you. It will probably take time, but once the kitten has a little more confidence he will come out from the sofa.