is this illegal?

My moms neighbor has a camera that's pointing directly onto her back porch. It's not looking at his land or his property at all. Nowhere near his house. It's on the back of a barn and right behind the barn is the fence that separates his land from hers. So it's on his property but he's watching my moms property. That means he's watching my siblings play on the back porch. 
Is that illegal? What can she do to make him take the camera down? It makes me feel like he's a fucking pedophile.  I told her to get a privacy fence but she can't afford that right now.