That only works if:
1. the grandparents are retired and not as busy as the parents.
2. the grandparents are willing and physically able to spend hours each days educating their grandchildren, after already spending hours a day educating their children when they were younger.
3 the grandparents even live anywhere near the children.
It's not a grandparent's responsibility to educate the grandchildren, when there are healthy and able parents already in the picture. It's the parent's responsibility. Grandparents already made raising their children their priority, and are now preparing to retire, and do all the things they couldn't do when their children were young.. Most people look forward to retiring so they can travel and do all the things they had to put on hold to raise their own children. To ask them to now put their senior lives on hold to raise their grandchildren, when their parents are perfectly able, to do so, is a bit selfish of the parents to even ask, in my opinion. If a parent is too busy to educate their own children, then that is their choice and they need consider reprioritizing their lives to make their children a priority over whatever else has them too busy to be a parent.
Most Grandparents are still working while their grandchildren are growing up.
Before our first child, my wife and I decided that she would be a stay at home mom. We learned early that we could live on one income, and planned our budget on that income. We also decided that the family would take all meals together (unless I was out of town), and that we would focus our discussions on our children. During the times that I was out of town (happened frequently), my wife carried on our plan.
Friday night was always parent's night out. Saturday was Children's day. Sunday was the Lord's day. The entire week (including weekends) belonged to the Lord, and God was a frequent topic.
Our children were far from perfect, and didn't leave the nest on fire for God, but they had a sound foundation. When I look at our grown grandchildren today, I'd have to say that, even though we didn't approve of their method, they did a good job raising them.
Everyone! Teach your children about God, live you life for God, and read the Bible to them and with them. If you don't, the only God they will ever know is the world (Satan).