Remember those days when your children left home to start their own lives?
For two or maybe three decades your children had always come first. Schools, sports, birthday parties, sleepovers, etc. Their schedule was your schedule. There was always something involving them that was elevated to priority status. Eventually though, they cut the cord either by college, marriage, job opportunity or simply wanting to be on their own.
Finally, you could take a deep breath, sit down in the recliner and pursue whatever you had been putting off for years. You looked forward to hobbies, extended vacations or even catching up on the books that were sitting on the shelf, unfinished and gathering dust. It was time to get your weekends back.
With all the time you suddenly had on your hands you began inventing things to keep busy. Furniture was rearranged. All of the spices, jams, jellies and sauces were checked for expiration dates. Garages were cleaned out. You set up a table at the neighborhood garage sale. If it didn’t sell it was donated.
Perhaps you even started thinking about relocating. Maybe a smaller home nearby or moving to a friendlier climate.
But then, one day after that, you got the news…a new generation was on the way. 
All at once everything changed. Now, new parents had to be helped. Their schedule was once again your schedule. No phone call went unanswered.. Plans about possibly leaving the area were put on hold or filed away for some time in the distant future.
Soon you had small children with you, even if only occasionally. Once more your house needed rearranging. Gates were installed by stairways. Anything hazardous was placed out of reach.
This time though, having children was different. You generally got them on their best behavior. They really enjoyed being with you. No wish of theirs went unfulfilled and you were paid back with love. When it was time for them to return home, they were sorry to have to go and you were sorry to see them leave.
In time, it wasn’t unusual for you to become closer to your grandchildren than you were with their parents.
Was it because, since they weren’t living with you, time with them was always pleasant? Surely that contributed to a happy relationship.
Could it be, whenever they visited, you had treats for them that they seldom had at home? No doubt it was something they looked forward to.
How about when they had dinner with you? It was no problem if they didn’t want to eat their broccoli.
Strict bedtimes when they stayed overnight or for a long weekend? Not with Grandma and Grandpa. Bedtime was flexible.
All of these situations share a resemblance. It was much easier and more fun for your grandchildren to visit you than for them to be at home.
So, back to where we started. Why do grandparents and grandchildren get along so well?
The answer is obvious. They get along so well because they have a common enemy!