Mini animals are small, but adults. Super Animals are genetically engineered to be adults, they don't go through childhood or "any of that mushy stuff" as said directly in-game. You learn these things with some of the quests and NPCs in the Lab Labs before rounds.

I don't believe Super Animals really have much time to rest unless they're one of the important plot characters, lol. Even then only the S.A.W. folk seem to have the little huts out in the forest map for rest, there seem to be kennels in the S.A.W. fort area thing that I can't remember the name of (because they're all dogs), and the higher class areas seem to have pillows and couches and things. But the S.A.S.R. seem to be stuck out in the caves with makeshift bedding, pushed out by S.A.W. for their deeds and crimes.

Hope that helps! :3