Definitely at least 2 generations in my family. I spent a lot of time at my grandparents houses as kids but they were not actually doing any childcare.
I think it also has to do with living further away from family becoming more normal. My parents swapped a lot of parenting time with my aunts & uncles - most of us lived within the same 3 town radius. I now live almost 5hr drive from my family so we can’t just swing by Uncle’s house for a few hours.
Having kids later makes sense too - my MIL is almost 70 and my dad & FIL are 65, and we just had our first kid. I’m turning 30 next month so I’m still pretty average age but definitely not 18 like my grandma was for her first!