According to the insurance company Aviva, overall, grandparents save parents over $50 billion dollars just by looking after their grandchildren free of charge.

Other findings from the insurance company's study finds that 50 percent of grandparents charge no money for babysitting their grandchildren, and, on average, grandparents watch two children at a time for about 13 hours a week.

Grandparents are such great babysitters that 30 percent of them cancel their own plans to watch their grandkids. And, according to the study, 88 percent of grandparents feel closer to their grandchildren because they are able to spend more time with them while they babysit.

Although national Grandparent's Day isn't until September, make sure you show them how much you appreciate what they do for you.