Learn French: Leur maman travaille dans une entreprise.

In French, possessive adjectives match the thing being owned, not the owners! Even though there are multiple children (the owners), they share one mom. Since maman is singular, we use the singular leur. If they had multiple moms, it would be leurs mamans.

"Their" implies multiple people, so why does the verb travaille end in "-e" instead of the plural "-ent"?

The verb always matches the subject doing the action. Here, the person working is the mom (maman), which is a singular "she" subject. The word leur just tells us whose mom she is. So, we conjugate travailler for elle (she), which gives us travaille.

Why use dans for "at"? Doesn't dans mean "in"?

Yes, dans literally means "in" or "inside". While in English we usually say someone "works at a company," in French you typically say that you work in a company (dans une entreprise).

Do I connect the words dans and une when I speak?

Yes, you do! The letter 's' at the end of dans is normally silent. But because the next word (une) starts with a vowel, you make a spoken connection called a liaison. The 's' links to the 'u' and makes a "z" sound, sounding a bit like "danz-une".