1)
Why is "Ateres Zekenim Bnei Banim"?
1.
Rashi: This is when they see their grandchildren going in the good path.
2.
Malbim: The Nefesh of a person endures [forever], and regarding the body the species endures. This is the crown that grandchildren give to their grandparents. Old age is a sign that he is about to pass from the world; grandchildren will remain in place of them.
2)
Why is "Tif'eres Banim Avosam"?
1.
Rashi: When the parents are Tzadikim, this is the glory of the children.
2.
Malbim: The children exist in the merit of their parents, and their merit stands for their children after them.
