The impression I got is that this boy is left to do whatever he wants so as long as he is not "bothering" his mom. When I was little, I was able to play all over the neighborhood, so as long as I told my mom where I was going and who I was playing with. It's a matter of getting street smarts that way. But honestly, these days, I would not have my son if at 5 do that. It seems that his mom could really care less as to what he's doing and he needs to understand respect and boundaries especially with property. When I was about that age, I picked all the flowers in the front of our neighbors house because they were pretty. However, I did get in trouble because those flowers were not mine and did not belong to me.
It takes a village to raise a child, but these days, it's more like "I don't want to get involved as it's not my business" kind of attitude. I think if more people took to the village idea, maybe some things would stop.
Is there anyway, your street can put together a neighborhood picnic or something to get to know everyone? Usually I find that neighbors that keep to themselves have some drama in their life that they don't want to discuss with others if they happen to be friendly. Otherwise, I would just walk over and talk to the mother with what's been going on and to offer that if she needs help of any kind to not hesitate to ask since you mentioned she is a single mom. The worst that could happen is that she would not like you, oh well. Next step would be to call the police if nothing stops.