DW and I babysit the GK's and GM for the pure satisfaction of helping out.
We babysit our grandchildren as well.
While it helps out our son and daughter-in-law, we probably get more out of it than anyone else.
Yesterday, we took our 4 year old grandson to tour a submarine. He loved it so much we went through twice.
And of course I got to play in a submarine. How much fun is that?