Learn Russian: Дети дома. - The children are at home.

In Russian, the verb "to be" is almost always left out in the present tense. So instead of saying "The children are at home," you simply say "Дети дома" (Children at home).

Wait, isn't the word for child ребёнок? Where does дети come from?

Yes, ребёнок is the singular word for "child." However, it has a completely irregular plural form. When you want to say "children," the word changes entirely to дети.

Why is it дома instead of дом, and why is there no preposition like "in" or "at"?

The word дом means "house" or "home." When you add the -а to the end to make дома, it acts as a special location word (an adverb) that means "at home." You don't need a preposition like в (in) because дома already includes that meaning.

Does дома just mean "at home", or can it also mean "houses"?

It can mean both, but the pronunciation is different! When the stress is on the first syllable (до́ма), it means "at home." If you stress the last syllable (дома́), it means "houses" (the plural form of дом). In this sentence, you should stress the first syllable.