This is a very interesting drawing. The mere concept of only showing one half the horse is remarkable. For obvious reasons it has been drawn by a child, not a professional artist. Even a primitive drawing (e.g. a cave painting) by an adult would probably include the whole animal. There is no evidence that this child didn't intend to draw it this way (i.e. making the back part of the horse small so that it was included on the page.) Just interesting.
Notice how children are frequently anthropomorphic, i.e. the crab has to have two legs and two arms.
I did not ask what was in the crab's claw, could be an iPod. It looks like the scenario is either Disneyworld (Magic Kingdom Castle in which my niece once managed the restaurant) or, more likely, an aquarium. If you are interested in aquarium animals, Google the Mantis Shrimp.) Please note the claws on the submarine.
If not two, then lets have lots of legs. That is why this crab is called "Crab Rockerfella"; especially appropriate during this season at a certain Center in New York (hint: dancers)
These fish look like they have "flat top" haircuts. This will only be significant to old geezers like myself. But they are right out of the 50's.