D.B.
Children's museum - get passes from the library. There are usually exhibits that appeal to different ages, so get the kids to share some time in one, then the other.
Aquarium, same deal.
Simple stuff like nature walks or beach combing - take a bucket and pick up interesting stones, bring them home and wash, let dry, and paint. Give Grandma and Uncle Joe a paperweight, or put them on the balcony in flower pots or in a garden as decorations. In the late summer, find pine cones and tie a loop on them, put peanut butter on them, then roll in bird seed: poof! Instant bird feeder. Collect leaves in different shapes and make collages or spray paint on them as if they are stencils. Get a craft book or camping fun book at the library - great ideas from books from the 50s and 60s before everyone did everything on a computer or an iPhone.
Don't feed the ducks bread though - it's really bad for the ducks, it interferes with their ability to find healthy food, and their excrement fouls the water. (I know, I know, I enjoyed it as a kid, but it's pretty much forbidden in all responsibly managed ponds.)
Firehouse is great - our firefighters let the kids climb in the truck, learn about the helmets and masks, and look in the ambulance.
Farmers markets or farm stands - seeing real food growing also increasing kids' willingness to eat new foods.
Scavenger hunts with another family's kids - hide fun things in the park or the yard. Get those plastic Easter eggs and put stuff in them (chocolate kiss, hot wheel car...) and tuck them in shrubbery or notches of trees.
Thrift shop or flea market - find dress up items, things to create costumes, or props for imaginative play.