R.L. Stine 
Attack of the Jack! 

In this spinoff to the New York Times-bestselling Goosebumps series, two siblings rescue their uncle when he mysteriously turns into a Jack-in-the-box.Devin and his sister Violet are visiting their Uncle Jack for the summer. He lives in an old house by the seashore. Jack was a sailor and he has collected strange and fascinating items from the sea. Exploring a back room, Devin and Violet discover a locked trunk. A pirate’s chest. The trunk is wrapped in old, heavy chains and locked with a huge rusted lock. But they manage to get it open. They lift the lid slowly-and see that it’s filled with antique jack-in-the-boxes. Huh? One box is hidden under the others, covered in dust. It plays an odd unpleasant song. Up pops a very ugly, mean-looking puppet, an old pirate with a dirty red bandana over his long greasy hair, scars on his cheeks, and a beard, and one eye missing. "Thanks for letting Sailor Jack out!" he rasps, bouncing on his spring. Devin and Violet have a troubling question: Now that their uncle has been turned into a toy, how will they get him back?