Fablehaven...

Fablehaven is a great action and adventure series by the legendary Brandon Mull. He has three books in his series, they are

-Fablehaven
-Fablehaven 2 Rise of the Evening Star
-Fablehaven 3 Grip of the Shadow Plague
-Fablehaven 4 Secrets of the Dragon Sanctuary
-Fablehaven 5 Untitled...

So the series are about these kids named Kendra and Seth who go to live with their grandparents while their parents go on a cruise. Little did they know that mythical creatures were living in the woods behind the house...