So not just fantasy, but an introduction to fantasy... Could start small with a good short classic like Jeremy Thatcher Dragon Hatcher. The Artemis Fowl books make for good intro books I think.

If they are up to something with a bit more reading, I would highly suggest the Age Of Fire series by E. E. Knight. They follow the adventures of three dragon siblings. The first is the brother, the second follows his highly intelligent sister, and the third the crippled brother. It continues on, but the first three are on the same timeline, with each of their unique adventures.

On a side note, have you also considered light novels?