Also they may not be sure how many seasons would be produced and despite the how many years go by before Eddie finally turns human, he can still be a teenager without everybody questioning it or realizing that he is a different actor. Course in this case it may be a guess.
Two things have always bugged me about this series. One, according to the Drifter in that episode where Eddie helps a girl dog he has a crush on complete her deeds, Eddie's parents have completely forgotten about him. And this isn't apparently some magical thing, either, because that girl gets to go back to hers when she turns human. Is Eddie Squee!'s older brother or something?
It could be that the parents forget about the kid while he's a dog, but when he's turned back, they remember again.
The second is the pound episode, where it is revealed that dog tags can protect you against toxic gases. And conveniently, pounds leave these lying around inside of the chambers that they flood with gas to kill the dogs.
When the employee saw the dog tags, she realized (to her immense disappointment) she couldn't gas the dog because they mean it's not a stray but belongs to someone; they weren't some magical anti-gas phlebotinum.