Magna-Tiles are the best third-birthday gift ever. It is so easy and satisfying to build all sorts of structures with them. These things rule! Ronan usually constructs houses for various superheroes (Superman's door is always on the ceiling because he can fly out), corrals and zoos for animals, and garages for his many small vehicles. I imagine that these will be in use for at least three more years.
Yes, they are plastic, and I'm assuming they're made in China, although I couldn't confirm that. We have two sets, one translucent and one solid. The latest set was purchased here. Google for the best price.