If you can make your UK home DVD multi-region then you could simply pick up some DVD's to watch while in the US and then bring them home and still be able to watch them. I think you would be able to get Bob the Builder over there, but I am not sure how Americanised it will be. If it is it may make it not the same for your son, from that point it may work better to see if you could persuade him to try something different while on holiday. Maybe Sesame Street, Bear in the Big Blue House, Wiggles, Stanley or Dora the Explorer?

It may also work in well then if he also meets some of the characters at the parks.