you never know, the child might be autistic and only sleep for a couple of hours a day and be very difficult to manage the rest of the time. If I was in that situation I would tell my neighbours but you can imagine the extra stress of having to worry about neighbours on top of the stress of having an autistic child. I think putting a polite note through the door explaining your distress is the best way to deal with it, they should tell you if there are any abnormal circumstances and if there aren't then they could try to be more considerate. As MP mentions above, converted flats and children are not an ideal mix. When my son was small we lived in a flat and we were extremely conscious of the neighbours when he made a noise or ran around but then what can you do? There are only so many hours a day you can spend in the park.