'The Mysterious Tadpole' and its Ability to Baffle Me

This morning I put a DVD on for the kids that I got from the library. A collection of Scholastic stories by Maurice Sendak that were animated. At the beginning of the disc there is promotional short that has a lot of characters from different books gathering together to watch a movie. Included was a pond that had a large green and orange creature. The workings of my deepest memories began to stir. I know that creature! It is from a story that I had read over and over with my brother when we were young children. What was it about? All I remember was the creature lived in a pool and there was a little boy that visited him at night time. I proceeded to spend the rest of the day trying to track down the name of this book. I asked Reddit and the only things the suggested were "The Water Horse" "Serendipity" and "The Beast in the Bathtub." I tried different combinations of sea creature, monster, sea monster, dinosaur, dragon, etc. Nothing was working. I was getting so frustrated and because I couldn't figure it out it was sucking me in even more.  Luckily I hadn't really been planning much of anything with the kids today. Even still, I was ignoring them a lot in search of this book. I eventually called my brother to ask him if he remembered. He did! But not the title. His memories were even more vague than mine were. I finally called my Mom and described it to her. At first, describing it to her she didn't remember. Then she said "Oh I think it was called Mr. Kellogg's Egg!" She still had the book and got it. It was actually called "The Mysterious Tadpole" by Steven Kellog, and the main character gets an egg at the end of the book. She started to describing it to me and it was all coming back. The little boy gets a tadpole as a present. The tadpole doesn't grow into a frog, but just keeps growing and growing until they finally have to put him into a pool. The little boy visits the creature at night to feed it cheeseburgers and play fetch with it by throwing a garbage can into the pool.  Now I can get on with my life!