...please tell me I did the right thing.

We live in a 6 apartment building, 2 apartments per floor, with a central staircase. We live on the bottom floor. I got home from the store with the baby and when I get close to the building, I hear crying. I get inside and see that it's the kid, maybe 3 years old- who lives on the third floor. He is standing outside his door, sobbing and wailing and banging on the door and calling oit for his Mommy. Since I had just gotten home, I waited a little bit to see if someone would let him in the door. They don't. He is still sobbing, banging on the door and saying things like "I want my Mommy" and "Mommy, pleeeeease open the door". My heart broke. I don't know them well but she is a young mom who lives with her Dad and there is ALWAYS yelling coming from.thier apartmentk and 2 years ago we called the police due to a party she had where they were smoking pot in the halls.

Admittedly, I watch too much Law and Order:SVU and thought Mom could be in trouble, or could be doing drugs and ODed or something. I didn't want to go up there and call out this Mom on what I feel was borderline neglect and not know what state of mind she'd be in. So, I called the police to come. They came about 30 minutes later (too long IMO) and the kid was in the apartment by then. They didn't even knock on the door, just walked upstairs, saw no kid outside, and left. Now, what if the kid walked out of the building and wandered off?? Wouldn't they want to just check and make sure everything is OK?

Anyway, what would you have done in this situation? Did I overreact? I was practically in tears listening to this poor baby!