Grandparents' Day is Sunday: Who knew? OK, other than the greeting card companies.

But, there are a lot of reasons you might want to say thank you. New research from the University of Chicago finds more than half of grandparents provided some sort of care for their grandkids.

"Grandparents are playing the role of safety net for American families this time around," Sandra Timmerman said. She's with MetLife, which just released its own survey on grandparents. It finds grandma and grandpa are shelling out for more than the cute toy they spotted at Kmart. "The top of the list are things like clothing, basic needs and education."

"What we find often is that grandparents will sacrifice their own retirement savings, many times they will not be thinking about their own financial security, if their grandkids have needs," said Amy Goyer, who is with AARP.

Not always the best way to go. Goyer says financially stable grandparents can be a great gift down the road.