We had a mobile for our son's cot but it wouldn't attach to the cradle that he was in for the first few months so didn't use it. When we moved him into the cot we put it on but it dangled quite low and he just spent the whole time trying to grab it! We were recently bought a new one, really nice and didn't dangle very low, put it on his cot - BIG mistake!! He just spent the whole time trying to get to it, and now he can stand in the cot (he's 8 months now) it was certainly a distraction from sleeping! If he wakes early in the morning he tends to chat to himself for a while then settle himself back to sleep, I'm sure that if he had a mobile it would just keep him wide awake when he should be sleeping. Maybe if he had had one from day 1 it might be a different story but in my opinion they are definitely too stimulating and a distraction.