Free and easy with kids
You don't need to book much. Waterfront Park has the Pineapple Fountain, which doubles as a splash pad on hot days, so bring a towel and let them run. The Battery and White Point Garden give kids cannons to climb on and open lawn under the live oaks. The City Market is stroller-friendly and good for a snack and watching the sweetgrass basket weavers. And the Angel Oak on Johns Island, a free, 400-plus-year-old live oak with limbs that rest on the ground, genuinely impresses kids in a way photos don't.
For a beach morning with small kids, Isle of Palms County Park is the easy one: restrooms, outdoor showers, a playground, chair rentals and lifeguards in season, about 30 to 40 minutes out, for a county parking fee of $5 to $25 by month. Sullivan's Island is free and quieter, 20 to 25 minutes away, but has no lifeguards, rental stands or snack bars, so bring everything with you. Folly Beach is livelier and the hardest to park on a summer weekend. The beaches guide compares all five.
By age
Toddlers and preschoolers: lean on the waterfront, the carriage ride, Magnolia's animals and the aquarium touch tank. Skip long house tours, which test small patience fast. Bring a carrier for the cobblestones.
Ages 5 to 10: the harbor and dolphin cruise is the sweet spot, along with a beach day and the Pineapple Fountain. Fort Sumter (a separate ferry ticket, $46 for adults on GetYourGuide; the published child fare is $26 for ages 4 to 11) works if they like history and boats. So does the USS Yorktown at Patriots Point, where kids 6 to 12 pay $23.
Tweens and teens: they can handle the deeper history, including a daytime carriage or walking tour, and most are fine on an early ghost walking tour by 11 or 12. Kayaking Shem Creek is a good outlet for older kids with energy.
To turn these into full days, the family version of the 3-day itinerary has the kid swap built in: the aquarium and the USS Yorktown in place of the harbor cruise, and Magnolia over the other plantations.