дитё is a slang for дитя, which is bookish or a folk word for "ребёнок" ("What have you to say, my child?"). It is not used much in modern Russian outside certain phrases. We are not keen on discussing stylistic choices for thousands of words here, so in this course we use "ребёнок" pretty much without any other alternatives.
The plural or "ребёнок" is "дети", though.
Thank you, very interesting. http://dictionary.reverso.net/russian-english/ребята
It is Отцы и дети. And yes, you are correct in the assumption this is an idiomatic translation. Oftentimes translating titles literally produces quite a boring phrase. Authors, on the other hand, usually do not name their novels "A book about a dude who dies". They try to make the title short and vivid, which the translators take into account.