Well, the djinn is now free again, and professor Jones promised to help, so Devon will probably be able to be restored to an older kid, isn't it?
Then, the little malicious witch learned the restoration spell, so she may be able to restore him fully, although I guess it would be better story-wise to somehow prevent it, as growing back would separate him from his girlfriend, and their relation has been a constant cute and well made _link_ between several stories. ^^
Besides, the evil little witch is, well, evil, and don't seem to be keen to really helping anyone. I would rather bet on her tricking characters than anything else.
There also quite obviously the ending here leaving it quite open to another story focusing on the fairy doll, as I bet you wouldn't leave Thea like this, yet don't imagine it just being a simple restoration, would be too easy.
Finally, with Bobby being recognised as a wizard, able to go to a magical school, and seemingly gifted in the art of age changing potions, I would guess we may see more of him.
Got anything right?