It depends whether you were speaking about the subject before. Then you use ona, ona, oni and similar. But in this case you can also use "Je to..." or "Jsou to...". (Ony) Nejsou malé holky. and Nejsou to malé holky. are pretty much equal.
If you see something for the first time, you use "To je...".
I'm not sure, exactly, what you're asking, but I'll assume it's about the adjective ending...
"Holka" is a feminine noun, and "holky" is its plural. The feminine plural form of the basic adjective "malý" is "malé." "Zvíře," however, is neuter, and its plural is "zvířata." The neuter plural form of the adjective "starý" is "stará."