If you have any kid books around, read him a story and show him the pictures as you read. Teach him a song like Itsy Bitsy Spider, The Wheels on the Bus, Twinkle Twinkle etc. Show him family photos if you have a photo album--especially photos of him as he has been growing up. Ask your son to give the child a couple of celery sticks, some raisins, some peanut butter and a butter knife and teach the kid how to make 'Ants on a log' and of course save one for Daddy.
If you have access to the public library, that was the age that my kids adored rhyming books like Seuss "Fox in Socks", "Green Eggs and Ham", "One Fish Two Fish" and non rhyming with beautiful pictures like Sendak "In the Night Kitchen" and "Where the Wild Things Are"
Before you end each session, tell him what you want to do next time and if he has been enthusiastic, ask if he is looking forward to it as much as you are. Send him kisses and ask that he share them with Mommy and Daddy from you. Find one positive to praise him for, but don't overload the boat--he sits still so well, he learned the song so quickly, he drew such a nice picture for you, etc. Tell him you are excited to visit with him tomorrow.