"I am a girl, he is a boy."
Translation:Eu sunt fată, el e băiat.
Because it's not necessary. The indefinite article doesn't work the same as in English. It's much more similar with how the French one works. In French there are circumstances where you can skip it. For example "Je suis ingenieur" - Eu sunt inginer - I am (an) engineer.
Andrei926539 (Moderator) said "In French there are circumstances where you can skip it. For example "Je suis ingenieur". Well, I agree that one can say "Je suis ingénieur", but still you must admit it is confusing for French speaking people because for fată (fille) and băiat (garçon) one must always add the "o" and "un". Examples: Mon nom est Paul, je suis UN garçon. Je m'appelle Sophie et je suis UNE fille.