What is the purpose of this? What plot will this lead into? You say that you see this as a long roleplay, but really, so far all you've mentioned is that they constantly change each day somehow. I don't think the mechanism is explained, so it feels like it's just happening just cause. And honestly, I don't see much story potential with what you described so far. It just sounds like the entire story amounts to "Littlefoot and his friends experience some changes. They return to normal. The end."
But what about conflict? What are they going to do each day? Are their parents going to recognize them? How are they going to react? What else did you have in mind for this roleplay outside of them just changing? And again, what is the meaning of the changes?
To explain, I'll bring up another roleplay. The change in species one that hasnt' been continued in a while, where the gang become sharpteeth. The purpose here was to explore what would happen if Littlefoot and his friends were suddenly on the opposite side of the food chain, and how their folks would react. This already bring about plenty of potential for story telling as it could go in several directions, and has already brought forth the well-recieved fanfic, The Seven Hunters, which was inspired by the roleplay.
But so far, you have only explained that these characters change, but you haven't reallly given a reason as to why. You haven't given a potential conflict. It's almost like your idea is just them interacting like they normally do, their parents interacting with them like they normally do, with the only thing changing being what they are. This does not make for a very interesting story.
There is potential, however. Like... let's say that, when they change into different species, their personalities are altered to suit that species. Cera becoming a bit more skittish and ready to fly off when she's a flyer, or laidback Spike turning into an aggressive fighter when he becomes a threehorn. Stuff like that. And having their parents actually react to the changes. Perhaps refusing to acknowledge that the 'colored like my child but a different species' child is their own. Like Cera's dad honest-to-gawd refusing to see a longneck Cera as his daughter.
These ideas could help spread out the roleplay and make it longer.
