I read this story in the mid 1980's. A young boy is staying with either his grandmother, aunt, some older female care giver. The shadows in the backyard are alive, and anything brought back there that throws a shadow creates a shadow object or individual. I forget what the conflict is, I think there's some kind of evil ruler of the shadow people.
Either a dolphin statue or fountain rules there. This book was awesome but I can't remember the title. I've done several searches online and have turned up nothing. Any information would be much appreciated.