"Four boys and many girls sleep."
Translation:Quattuor pueri et multae puellae dormiunt.
There are many different plural endings in Latin, and you have to learn the system. Puer is masculine, and masculines with the ending -er get in plural an -i: pueri. Puella is feminine, and the plural ending is -ae: puellae. The daughter languages of Latin have simplified this, like Spanish, which has a regular plural ending -(e)s. Italian, on the other hand, is closer to mother Latin: the masculine fratello (brother) is in plural fratelli, and the feminine strada (road) gets the plural form strade.