Looking it up online it seems the accent came from reimporting the French papa; in Latin both papa and pappa were the onomatopoeia for dad (and children's food, modern Italian pappa), but in Italian originally the form babbo was preferred (it still is in Tuscany for instance), derived from the Latin pappus (old man). "Il papa" without the accent is the pope.
You have such wit, Mabby! And thank you both for this discussion, I just asked this very question about mamma and papà on a separate sentence, and voila! here is the answer ... f. formica: once you take the time to really explain some concept / word / phrase, it would surely be awesome if duolingo could find a way to link to it when someone came across it in practice in duolingo.
That's true; if it followed the same derivation as "papà" it might have to do with trying to emulate the first syllables a toothless child speaks. Apparently it was originally papa in Old English too, and this usually trustworthy website seems to support the derivation from "father": http://www.etymonline.com/index.php?term=pope My source offers more options, but because of that it feels like it's grasping at straws; or to use the Italian idiom, "si arrampica sugli specchi".
"Ragazzi" can be translated as either "boys" OR "children" because the male form is used for the collective noun. A group of just girls is "le ragazze". A group of just boys is "i ragazzi". A group of children that include both boys and girls is also "i ragazzi".
il ragazzo + il ragazzo = i ragazzi, la ragazza + la ragazza = le ragazze, la ragazza + il ragazzo = i ragazzi
"I bambini" is also fine for "the children". I am not a native speaker, but from my understanding "bambini" simply implies a much younger child than "ragazzi" does. "Ragazzo" can be an older guy as well. I don't think Duolingo should mark you wrong for using "bambini", nor for translating "i ragazzi" as "the boys". "Le bambine" however would only ever translate to "the little GIRLS".
In my opinion it would be great if Duolingo allowed you to choose between a few common variants of English such as British, American and Australian English. They could do the same for other languages that are slightly different in different places (for example Spanish, they currently only teach the American version) and it wouldn't be too much work as they would usually only have to change a few words.