There is a magic age around 18 months, I think, if you expose a child to something they can get really obsessed. For Roman it was the Thomas train set he got for Christmas at 18 months old. For Charlie, it's going to be Cars. Not just regular cars, although he likes them too. Cars as in Disney Cars, Lightning McQueen, Mater, etc. We have a whole collection of plastic McDonald's Cars given away when the movie came out a few years ago. We also have some metal ones given to Roman, and even some Duplo versions. There are two, especially, that Charlie must have within a few-foot radius of himself. That's metal Lightning McQueen & Sally.
At mealtimes. In the car. At the grocery store. In bed. We cannot lose these precious Cars.