Calvin And His Dump Truck

This is my exuberant 4 1/2-year-old neighbor who is very, very proud of his new dump truck.  He even put a monster face sticker on the windshield.  He's a really sweet little guy and has now taken to knocking on my door to see what I'm doing in the evening and I have a feeling he's going to make a habit of it.  Since it's my glass door to the back patio, I can't hide from him so I'm trying to think of ways to interact with him but to be very honest, I'm not the best with kids.   If any blippers have a suggestion, I'd appreciate a little help.