balavac

1. colloq. derog. brat; whippersnapper; snot-nosed kid
   Neće mene neki balavac da uči pameti! — No snot-nosed kid is going to lecture me!
   Ti si još balavac, ništa ne znaš o životu. — You're still a kid, you know nothing about life.
2. colloq. snotty little kid
   Ispred zgrade se igra gomila balavaca. — A bunch of snotty little kids are playing outside the building.

For a girl, the word is balavica.