La carta es acerca de los ninos translated The letter is about the boys.In this case, why do you use "de"? That would make it "The letter is about to the boys?
"acerca de" is a phrase that means about. "de" is not an 'additional' word in this case.
I'll give you some examples La carta es acerca de los gatos: The letter is about the cats La carta es acerca de la naturaleza: The letter is about nature La carta es acerca de ella: The letter is about her
Some phrases are not translated exactly word for word. Acerca de is a phrase that doesn't translate perfectly word for word to English. It does mean "about" and both words are required for it to be grammatical.