It's not about a grudge God holds. It's about straightening up and raising our kids to obey God rather than raising them to be wicked. Wicked people tend to raise wicked kids. I'm sure you've heard "children learn what they see." The sins of the parents are often visited upon the kids in a couple ways...First, the kids imitate their parents, and in that way, evil doesn't quite beget evil,but rather cultivates it.God holds grudges for 3 or 4 generations...I don't find that loving and forgiving. Jesus did say Love your enemies, do good to them which hate you. Yet God visits iniquities of the father to the children of his children...and his children...and his children.
The magic of The Bible is that it takes years of study to know what the words people can read for themselves actually say...
Punishment accompanies sin that one will not repent of. And God is saying that He will allow it, (he allows us to choose our own will) but they'll be punished accordingly. And second, sinful behavior of someone tends to yield natural consequences that not only the sinner but his family ends up enduring.And God will allow it.
But He also says right there same place.....those that love Him....which surely includes a child who rejects his parents' evil ways and chooses to obey God....will be shown mercy. The children's redemption is not only possible, but welcomed by God. God speaks about the reward right there in the same passage. It's not about a grudge. It's about reaping what you sew.
Jesus doesn't contradict the Father when He discusses repentance. He reiterates.
And yeah, Jesus says love your enemies. He explains that in the past we were told to love our neighbors as ourselves. Now He's talking about loving our enemies, too. That's not a contradiction. God spent generations raising us to the age where we could receive a commandment like that. If you look at the passage in the Gospel about marriage, where Jesus teaches that divorce is no longer permitted, He's asked why He says this if the law permits divorce. He explains that in the past, their hearts were too hard to accept this part of the law.