You are partially right, it means diminutive, and diminutive often translates to "small" in English, but it's dziewczyna -> dziewczynka

and ciasto-> ciastko-> ciasteczko in nominative singular form and o changes to a for plural (and accusative=nominative for neuter nouns)

https://pl.wikipedia.org/wiki/Zdrobnienie#Formanty_o_podstawie_-k-

Yup, added.