The Gates of Atlantis Series

Thirteen-year-old Colin knew nothing of the magic world until he was bitten by a mischievous pixie. He meets thirteen-year-old Alleya on a secret website devoted to magical creatures. Before he knows it, Colin finds himself thrust into a whole new world. Alleya has been hidden away from the rest of Atlantis because she's half-mermaid, half-Atlantian. Her father tries to ease her boredom by getting her a computer and finally allowing her to go to school. She accidentally lets slip a dark secret - the gates to Atlantis are being shut and it's destroying magic. 

Callidora is an Atlantian noblewoman and member of an elite guard whose purpose is to keep Atlantis pure...until her life is turned upside down by the birth of a son. Phoibos, bullied and taunted by other kids, is sure of one thing: something is wrong with Atlantis. Impure Atlantian-Human hybrids are ruining his city, and he'll stop at nothing to rectify that. Callidora is the only one who knows the truth of who her only son really is, and how dangerous he can be. Can anyone stop Phoibos before his need for purification brings Atlantis to the very brink of destruction?