The Talmud source for this Halakha regarding screwing boys below 9 years, is Sanhedrin 54b https://web.archive.org/web/201703150...
Regarding killing of the Non-Jewish girl who was raped is not in the Talmud, Maimonides derived this Halakha on his own.
The Rav reads from Maimonides (The Rambam) Misheny Torah. The Girls is killed because a Jew fell into sin through her.
Screwing a boy is no offense if he is under 9 years of age, because he is not considered a man. If he was over 9 then it is considered sodomy, which is forbidden.
So pedophilia is allowed only with boys under the age of 9.
Sex with Non-Jewish females is forbiden and the punishment for the female if at least 3 years and a day is killing, but the Jew is only flogged.
It is not clear if punishment is inflicted on a baby girl under 3 years and a day and if whether the Jew is punished for raping such girl.
