Do I call police or CPS?

I don’t know if this is the right place for this, but I need help. Also, I’m on mobile so apologies in advance if there’s formatting issues.

After work today, I came to visit my boyfriend at his apartment complex. There was a small child in the parking lot alone with no type of supervision, and he was also not wearing any clothes or shoes. He was only wearing a diaper, which appeared to be filthy as I could smell it from about 10 feet away. I immediately look for someone, but there’s no one around. I finally see someone’s door open so I think he could live there, but when I talked to the woman that lived there, she told me he wasn’t hers but she knew where he lived. She knocked on the person’s door and informed her that her child was outside. The woman didn’t even seem to care or even notice that he was outside.

So now, I don’t know if this warrants me contacting the authorities. Could this be considered neglect? And if so, should I call the police or CPS?

I’m sorry this is so long, but I am very shaken up by this whole thing as it’s a dangerous area for a an unsupervised child.