It happened at White Crane Road and Bert Crane Road Friday.
The boy's foster father called Merced County Sheriff's Deputies to report the boy had killed a couple of the family's dogs.
The boy told investigators he threw one dog down an irrigation pipe after it tried to bite him, and then threw two other dogs down a smaller pipe. The top of the pipe was then covered with a chunk of cement.
The dog thrown into the irrigation pipe washed out into a canal but was able to make it out and return home.
The other two dogs are believed to have drowned.