The first book starts where the main character shows creativity, and is sent presumably to his death. He then ends up in a secluded area run by a caretaker where they learn to use their creativity and art as magic.
The two sides go to war, one led by the main character and the other by his twin on the other side. In later books, they learn that they live on an island in a chain, and multiple books deal with those other islands. They learn from someone from our world that they live in the Bermuda Triangle, and they also wrap around to the other side of the island chain if they go to the end via a giant waterfall.
Some random things in there are magical sentient whiteboards and statues. A sequel series was released recently, detailing the children and their adventure. That's about all I can recall, can't remember names of anything.