I prefer to let them( grandchildren) know ahead of time so they can savor the wait & have something exciting to look forward to. However, my daughter, their mother, loves surprising them. One year we went we started our trip over New Years & the last present they opened at Christmas had t shirts for them. The print was backwards on the shirts so they had to put them on & look at themselves in the mirror to reveal “ we’re going to” on one & “Disneyworld” on the other. Their reaction was great!
Two summers ago, we drove to Florida from Texas & stayed at the beach for 3 days. When it was time to leave to go home, we went on to Orlando instead of home. They were absolutely clueless. As we got closer & closer to DW, we kept asking them if anything looked familiar. One fell asleep & the other one finally realized where we were & began screaming & waking her brother up. He didn’t believe his sister! Their reactions were share-on-social-media-worthy, even though we didn’t! It was really fun & funny for us all!