Loss of Children, as a form of Divine punishment: Berachot 5a-b, Shabbat 105b
For Parents who are Rebellious against Hashem: Ketuvot 8b
For Parents who speak foul speech: Ketuvot 8b
For Parents who don't mourn the death of a good person: Shabbat 105b, Moed Katan 25a
Punishment of Children for their parents, in general: Berachot 7a
Punishment of Parents for sins of their children: Succah 56b
