Advice on handling neighbor situation

I’m looking for advice on how to handle a situation that’s been going on for a few years.

There is a teenage boy (I’d guess around 16–17 years old) who lives in my mom’s neighborhood. His parents told us that he has autism, and I completely understand that this may affect his behavior. I’m trying to figure out how to handle a situation that has become increasingly concerning.

Every summer for the past few years, he’ll stand on the sidewalk outside my mom’s living room window and stare into the house for long periods of time. He’ll sometimes stay outside for hours. The sidewalk runs rig ht along the main road through the neighborhood.

This year, though, it’s escalated. He’s started hopping over the gate and coming much closer to the house, walking up near the windows and even close to the front door. There have also been multiple times where he’s followed us while we’re walking our dogs, making comments about the dogs or repeatedly saying hi and continuing to follow us until we respond.

We’ve tried talking to his parents. They spoke with us once and told us he has autism, but since then we’ve tried knocking on their door multiple times and they won’t answer. He’s almost always outside by himself, not supervised.

At this point, our concern is that he’s entering the property and looking into windows and approaching the doors. It feels like a significant invasion of privacy, and we’re worried he’ll continue getting more comfortable coming onto the property.

Has anyone dealt with something similar? Is there anything we can realistically do? Would calling the non-emergency police line even accomplish anything, or is there a better approach? We don’t want to get him in trouble, but we also feel like my mom should be able to feel safe and have privacy in her own home