Here's why:
* Multicellular: All animals are composed of multiple cells.
* Eukaryotic: Their cells have a nucleus and other membrane-bound organelles.
* Heterotrophic: They obtain nutrients by consuming other organisms.
* Motile: Most animals are capable of movement at some stage in their life cycle.
While there are many other classifications within the animal kingdom (like phylum, class, etc.), the kingdom Animalia encompasses all of the organisms you mentioned.