The lollipop kids

"Years ago, early settlers locked these monsters away in a secret prison deep in the woods of New Amsterdam so they would never return to the Old World again. Those woods became New York's Central Park, and now the monsters have escaped! Nick, age fourteen, finds out that he is a "legacy" to a secret society that, for the last 400 years, has kept these monsters in check. He and a ragtag group of kids just like him have to put the monsters back before they get out of the park and destroy the city"--Provided by publisher.