You need Dave and Becky!! When Curtis was about the same age as your nephew he discovered the Dave and Becky There Goes series at our local Hollywood Video, I found several of thier DVD's online at Amazon.com and purchased them for his Birthday..
They have There goes a Monster Truck, its extrememly kid friendly, its geared towards kids 3-8, Dave is a goof ball, and while I enjoyed them the first few times he pretty much wore me out on them! But he loved them!!
Thier company is called Real Wheels.. The adventures I found came 3 to a DVD or 1 to a VHS and we bought Rescue Adventures with There goes a Rescue Hero, Police Car, and Rescue Vehicle..
Truck Adventures with There goes a Fire Truck, Garbage Truck, and (Big Rig) Truck... Travel Adventures with There goes a Train, Plane, and Bus, we had a 4th DVD with There goes a Monster Truck and two others on there, its either gotten lost in one of our moves or my sweet baby angels broke it! but on VHS we have There goes a Helicopter, and There goes a Motorcycle..
The videos are informative, but set in a way that its keeps the young ones attention..
Good luck on this too!!!
X.