No idea on author but story from probably before 1960 and more likely earlier about a boy who gets stuck in a very realistic dog costume and ends up be adopted by an abusive "owner" -- last scene is the guy kicking the kid in the ribs. For some reason, costume or "dog suit" prevent human speech, I guess. Not sure if this is addressed.
The kid took him upstairs and into a kitchen. "Hey, Ma," he said. "I brought home a mutt."
"You get that frigging mutt out of here before I cut you open," said the kid's mother absentmindedly. Lester slunk off into another room with his tail between his legs. In the other room there was a man drinking out of a bottle who kicked Lester in the side.
Lester went out into the hall. He decided he didn't like it here and that he ought to get out of his dog suit.
But the zipper was stuck!
He tried and tried, but he couldn't make it budge. What could he do? Maybe if he went home his Uncle Fred could take him back to the factory. Anyway his mother could always call the fire department. But he didn't know how to get home. He would have to ask the kid and his mother for directions.
He padded back to the kitchen. He laughed to himself as he thought how surprised they would be to hear him talk! As he came into the room he heard the mother say, "Okay, okay, okay. But he's got to eat garbage and nothing but garbage."
He said, "I realize this will come as a shock to you, but I am not a dog at all. I am a boy named Lester and I live at 233 Hummingbird Crescent and I am entering the fifth grade next autumn. Uncle Fred gave me this dog suit but the zipper is unfortunately stuck. May I inquire directions to my house? I want to see my mother and father again. X²-√(4Y) (3Y/X)=7."
The mother clapped her hands together and said, "Listen, he's trying to talk."