Visit a farm. Your kids will get to visit with all of the animals, and you'll have a chance to pick up farm-fresh eggs, milk, or produce.
Pick some berries. You can head to a pick-your-own farm, or, if you know of any wild bushes in your town, check out those instead. (Of course, make sure you know what berries are edible and what's potentially poisonous!)
Visit a new-to-you park or playground.
Clean up your town. Grab some gloves, grabber tools, and garbage bags and head to a public park or beach to do some Good Samaritan work. Just watch your kids closely to make sure they don't try to pick up anything dangerous.
Go fishing.
Go for a nature walk.
Go to a baseball or other professional (or semiprofessional) sports game.
Go for a family bike ride. You can stick to your neighborhood for this one, or check out local trails.
Catch fireflies. If you're lucky enough to see lightning bugs in your backyard, you can stick close to home. Otherwise, head to a public park with some mason jars and let your kids run after the magical bugs (but be sure to release them right away, of course.)
See the cherry blossoms. It's the perfect time of year for the beautiful blossoms. Google "where to see cherry blossoms near me" and head out. If there are none in your area, check out a nearby botanical garden instead to catch spring blooms.
Go for a hike.
Go on a family adventure race. These family-friendly "races" have popped up everywhere in recent years, and they're so fun. Google options near you. There might be an obstacle course race, a color walk/run, or a costume walk/run your kids will love.
Take an aimless drive. Find a scenic route, roll the windows down, cue up your kids' favorite tunes, and have a springy sing-along drive. Consider having a few spots in mind where you can pull over for pictures or an ice cream pit stop.