Penelope Gilbert and the Children of Azure by Emily A. Steward

Mixed children of mortal and magical parents are referred to as Pythians. They hail from the land of Azure, but some of them were sent to Earth (a.k.a. Terra) for protection. What’s worse is that the evil Lord Esmond sends his henchmen to various schools to sniff out children with such powers; he wants them eliminated. It is not long before most of them are captured and sent to Azure for slaughter. Four who managed to escape, Penny, Crane, Pete, and Haldor, know that they have to try and rescue the others. Though they have a strong will to survive, they are going to need a lot more to successfully execute their rescue mission. Penelope Gilbert and the Children of Azure is a gripping story full of excitement, and it leaves its readers begging for more!