Collective numerals in oblique cases

In Polish, counting mixed-gender groups or young beings (like children, siblings, or twins) requires collective numerals (dwoje, troje, czworo, etc.). Declining them into the oblique cases (Genitive, Dative, Instrumental, and Locative) introduces a specific set of suffixes and an unusual pattern for the accompanying noun.

Here is the pattern using czworo dzieci (four children):

CaseNumeral SuffixNoun CaseExample
Genitive-gaGenitiveczworga dzieci
Dative-guDativeczworgu dzieciom
Instrumental-giemGenitiveczworgiem dzieci
Locative-guLocativeczworgu dzieciach

The Dative Case (-gu)

In the Dative case, the numeral ends in -gu, and the noun matches it in the Dative case.

The babysitter forbids the four children to stand on the seats.
Opiekunka zabrania czworgu dzieciom stać na siedzeniach.

The Genitive Case (-ga)

In the Genitive case—often used for expressing absence (bez) or destination (dla)—the numeral ends in -ga, and the noun takes the Genitive case.

We need a larger car for the six siblings.
Potrzebujemy większego samochodu dla sześciorga rodzeństwa.
I won't go anywhere without the five children.
Nigdzie nie pojadę bez pięciorga dzieci.

The Instrumental Case (-giem)

In the Instrumental case (used with the preposition z, "with"), the numeral ends in -giem. Unlike the Dative and Locative, the noun does not match the case of the numeral; instead, it takes the Genitive case.

I am driving to the city with the two twins today.
Jadę dzisiaj do miasta z dwojgiem bliźniąt.
The babysitter is returning with the three children to drop them off.
Opiekunka wraca z trojgiem dzieci, żeby je odwieźć.

The Locative Case (-gu)

The Locative case (used with prepositions like o, "about") shares the -gu suffix with the Dative case. The noun agrees with the numeral, taking the Locative case.

We were talking about the eight infants in the child seats and how to fasten them.
Rozmawialiśmy o ośmiorgu niemowlętach w fotelikach i o tym, jak je zapiąć.