I will try to keep this short.
Neighbour, when we moved in, knocked on my door and asked if I understood about one of the keys for the communal areas. I assumed he represented the company that takes care of the building but I don't think that is the case, then soon after that I saw him sat close to the school, alone, watching us, on the way home from school with DS. Recently he leaves the building 30 mins before DS finishes school (DS doesn't finish at the same time every day and walks home alone) neighbour came back 10 mins before DS arrived and then left his apartment again so he could pass DS on the stairs. Next day, I decided to collect DS, I saw neighbour leave at least 10 mins before me so when I left the building, I was surprised to see him waiting just across the street, he then proceeded to start following me. He is smaller than me so I could thump him but am I being paranoid? There have been other odd incidents.