Nika had one very bad flaw - she stole very often.  Sometimes she could steal food or sweets from the store, sometimes she steals toys.  Her parents taught her this, so she followed their example.  
And at one of Alex and Kirk's toy exchanges, she stole their toys.  But they noticed her and immediately ran after her.  Nika, although small, is not at all nimble.  Her theft was successful solely due to her stealth, but she often had trouble escaping.  So Kirk quickly caught her and asked to return stolen goods.  After that a long moralizing conversation awaited her about the fact that stealing is bad.  She was very ashamed in front of both Alex and Kirk, and after that she stopped stealing.  She was a very obedient girl.  And the boys forgave her.  Yet they understood that she was not to blame for such a feature of her temperament. >///<