Exodus 34:7 (NIV) says that God "punishes the children and their children for the sin of the parents to the third and fourth generation".
The NLT translation says "I lay the sins of the parents upon their children and grandchildren; the entire family is affected — even children in the third and fourth generations".
The NIV is very explicit that God punishes the grandchildren, while the NLT is much weaker in this respect.
I've always thought that the punishment of the grandchildren was simply an effect of the original transgression.
For instance, if a crack-addict has a child, that child is going to suffer physically and socially as a result of the mother's actions. And when that child has her own children, they too will often still be paying the price. This isn't a direct punishment from God, it is the predictable result of doing something wrong.
Does the original Hebrew word require that the punishment be a direct intervention by God, or is it reasonable to say that God is simply warning that the consequences of one's actions can last for generations?