I’m sure it’s not the same with everyone, but before my son was born, I was very worried whether I would be able to raise a boy. My world was profoundly feminine because all my closest cousins and siblings are girls. So, my knowledge and understanding of little boys was very limited, to say the least.
As your grandchildren grow, they need adults less and less.
If you enjoyed babysitting them when they were small, there are so many things to miss when they grow out of that period, and even more so when they start craving more independence in their teens.