How about a treasure hunt. You make up clues and they hunt all over your property for the items, at the end the one that gets the most wins a special prize, but grammy provides prizes for all who participates. I usually go to joanns and buy some crafts for them to do and they love that. Using our camcorder we make a movie to take home for the parents to see what grammy went thru. I only see my grandkids once a year so just being there with them no matter what we do is fun.