Dear Dianna,
You are so fortunate to have grandparents for your kids that love them enough to dote on them! There are some families where the gp's really don't care to be involved, much less babysit & spend much time watching them....I agree with the many posts that say, what happens at grandma's house, is special, and won't be mirrored at home.
My son spends 1-2 days a week at his grandparents' house, as they provide (free) childcare while I work. Between myself, my husband, and the gps, we have managed to care for him without daycare...very lucky indeed. I have had many discussions with my MIL about how much she likes to "spoil" my son, and we really find that the child is only "spoiled" or willful if you allow bad behavior at home. He is 5 years old & has known from a very early age that he can do certain things at gm's house that won't fly at home. She abides by my general rules/requests, but when I leave my son at her house, she is in charge. After all, she raised one kid, good enough for me to marry...even tho I don't always agree with her methods, gifts, foods...she always makes sure he uses his manners, and has a voice as well.
I read one post that talked about the parents needing to be the distributor of gifts from you...and I caution you, I TOTALLY disagree with that. That is so hurtful to the gift giver, to take away their joy of seeing the kids' faces when you give them a gift (birthday, Christmas, whatever), AND associating the gift giver with that present. My brother & sister in law do that. They don't let my niece open my presents to her, in front of me. They don't let me hold her. (she is turning 3 in Feb) They don't do holidays with us. They basically have set it up so that she doesn't want anything to do with me. It is very sad, for me, anyways. But how I feel with the gifts, is that they are so controlling, that they want all gifts to appear to come from Mom & Dad. It is awful, & please don't do that to your kids' gps, as they will be so hurt. Part of our joy as adults is seeing kids' faces brighten up when we bring them something unexpected!
If your kids have good hearts, as I'm sure they do, they will know that different places have different "rules" & behave properly at home, and at gp's houses.
Good luck!