I've noticed it myself.
When my Grandparents were alive there were always Aunts and Uncles and nieces and nephews present. There almost wasn't room in the houses for us all.
Then the Grandparents passed away, one by one.
The Aunts and Uncles became Grandparents themselves and had their own gatherings with their Sons and Daughters and children. Now they have great-grandchildren and the tradition carries on with each separate family unit.
Next thing I knew, Thanksgiving was just Mom and Dad and my brother and myself. Neither of us had children of our own so the gathering was small.
I didn't know, back when I decided to not have children, that it would affect the holidays so dramatically. We don't have that family gathering of Grandparents, Aunts (me) and Uncles (DB) and their (our) children.
Now it's hard to even bother with it. Don't get me wrong, we're still thankful...all year long, every day. But...what's the point in cooking a turkey for 4?
I'm glad you have your family with you this Thanksgiving Sharon! I hope they treasure every minute of it.