Diminutive Forms in Greek

Latin and Greek both have diminutive terms that one can usually identify by the inflectional endings of the words. Hence, we know that κυναρίοις is diminutive because if we consult a Greek-English lexicon, it tells us that the lexical form of the word is κυνάριον: the ending suggests that the word is a diminutive form. And, in fact, lexica tell us that κυνάριον comes from κύων, which means "dog." So you can normally identify diminutives by the endings.

On the other hand, I don't think that ὀλιγοπιστίαν is diminutive; rather, the "little" part comes from the prefix ὀλιγό that's added to the word for faith. One word that people love to use now is oligarch/oligarchy, etc. Ergo, we can see that the ending does not make ὀλιγοπιστίαν diminutive but a prefix has been added to indicate smallness.

For other uses of the diminutive, see John 13:33; 1 John 2:1.