This is the 2059th most frequent Russian word.
дети
Children.
Here, 'дети' is used as the main subject of the sentence, indicating the plural form of 'ребёнок' (child). It refers to more than one child who are collectively engaged in an activity.
Дети играют во дворе.
The children are playing in the yard.
In this sentence, 'дети' is in the prepositional case as 'детях' due to the prepositional phrase 'о своих детях'. It refers to someone's children as a possession or responsibility.
Он заботится о своих детях.
He takes care of his children.
The word 'дети' is used in the genitive plural as 'детей'. It denotes children quantitatively, indicating the presence of three children in a family.