Gilgulim and the Tikkunim may not exist as they were recently invented by the Kabbalists with no Torah source so it is not a good answer, the real answer is what I wrote. Also, I am aware what some of the commentators write, but I would modify or read differently what they write to say if the children do repent their is a good possibility of the sins being forgiven but it is not definite in my opinion. The proof is from Kain killing Hevel. Plus from every other case where the righteous suffer for no apparent reason. G-d specifically tells Kain that punishment for his sin will occur in 7 generations with no conditions, G-d did not say "if your decendants repent then I won't punish them". In fact, it was a definite punishment destined to occur if the 7th generation repented or did not repent. And if you tell me that G-d knew that the guy would not repent, then the Torah would still not use such definite language and make us derive wrong information, as every phrase is precious. It would have at least stated that the one who was killed was also a murderer, which is not true. Similarly, we are still being punished for the sin of the Golden Calf (remember the Koehen Gadol can't wear gold on Yom Kippur, why? didn't he repent according to you?) and for the sins that led to the destruction of the Temple, and for the sins of other Jews in our generation, but if most of us repent completely then G-d may have mercy on us and forget about these sins and restore us to our glory.