Learn Polish: Pięcioro dzieci czyta z nami książkę. - Five children are reading a book with us.

We use collective numerals like pięcioro with a few specific types of nouns, including mixed-gender groups and plural-only words. The word dziecko (child) is a special case: its plural form, dzieci, always requires a collective numeral rather than a standard one.

Wait, why is the verb czyta (he/she/it reads) in the singular when there are five children?

This is a tricky but essential rule! When a collective numeral like pięcioro is the subject of a sentence, the verb must be in the third-person singular. You can think of it as saying 'a group of five children is reading'. Therefore, we use czyta instead of the plural czytają.

What case is dzieci in this sentence?

It is in the genitive plural. Just like standard numbers from five upwards, collective numerals (when acting as the subject or direct object) force the noun that follows them into the genitive case.

Why does the sentence use z nami?

The preposition z (when it means with) always requires the instrumental case. The word nami is the instrumental form of the pronoun my (we), making z nami mean 'with us'.