My wife and I have done similar. We privately share photos. It took a bit for my mom to get over the fact that she can’t post pictures of her grandkids on Facebook but I was eventually able to explain why in terms she understood.
1. We regularly share photos through private photo albums. This allows her the same exposure to photos of the grandchildren as social media would.
2. We made it clear she's free to share photos with people via direct text messages. It adds a bit of friction and keeps the photos relatively private.
3. Explained that it's the right of our children to control their presence online (with some parental assistance). They aren't old enough to do that so until then, please don't share.
4. Emphasize many times that it's about protecting and empowering our kids. It's not about preventing her from showing off her grandchildren.
I’d been printing off photos in various sizes (wallet to 8x10) and sending them along to my parents/grandparents - but it does take more effort to follow through. I do post photos of kids to a private account but maybe once or twice a year.
Ironically she switched to an android phone because she had too many photos I think and was always running out of storage. Of course the new phone had no photos, and her old phone would have been just fine if she was happy to start over too.
As soon as anyone visits their house, they immediately see recent pics of the kid.
It's been a big winner.