četvoro

1. (of mixed groups, children) four
   Imaju četvoro dece. — They have four children.
   Nas četvoro idemo zajedno na more. — The four of us are going to the seaside together.
2. (used on its own) four people
   U nesreći je povređeno četvoro. — Four people were injured in the accident.

The noun after četvoro is in the genitive: collective nouns take the genitive singular (četvoro dece), ordinary nouns the genitive plural (četvoro studenata — men and women together). It is also used on its own, without a noun: nas četvoro, povređeno je četvoro.