Learn Spanish (Latin America): Las niñas necesitan computadoras.

Because both niña (girl) and computadora (computer) end in a vowel (the letter a), you simply add an -s to the end to make them plural, giving us niñas and computadoras.

Why is it las niñas instead of los niñas?

In Spanish, articles (words like "the") have to match the gender and the number of the noun they describe. Since niñas is feminine and plural, we must use the feminine plural word for "the", which is las.

Why does the verb necesitan end in an -n?

Necesitan comes from the verb necesitar (to need). Because the subject doing the needing is las niñas (which counts as "they" or ellas), we use the plural verb ending -an. If it were just one girl (la niña), the verb would be necesita.

Why isn't there a word for "the" or "some" before computadoras?

Just like in English, when you are talking about things in general or an unspecified amount (they need computers, not the computers), you can just use the plural noun by itself after the verb without adding an extra article.