"Those girls are very pretty."
Translation:Esas chicas son muy bellas.
I don't think it is wrong. In fact, it's arguably the best translation. I've reported it.
I put that too. Just checked it on google translate and it comes up as - those children are very nice.
Does "ninas" only refer to young girls who we would consider children, whereas "chicas" can refer to older teenagers and above?
Apparently, that depends on where you are in the world. In another discussion, RyagonIV provided the link to a great chart: https://es.wikipedia.org/wiki/Anexo:Diferencias_de_vocabulario_est%C3%A1ndar_entre_pa%C3%ADses_hispanohablantes#Personas_y_oficios_(1)