If you’d rather not work for your nautical miles, NYC has a wide range of ferries that can take you to fun spots, or just for a scenic cruise.  NY Waterway runs multiple trips to the city and parts of New Jersey on the Hudson, and from terminals in Brooklyn and Manhattan ranging from 34th Street to Governors Island, where you can find lots of arts and activities on the weekends.  Kids under 12 ride free, and fares start as low as free or $1 - $2 for senior citizens and adults.  NY Waterway also offers packages with discounts on local tours and attractions; they even have an app to help you schedule your trip.
NY Water Taxi and its sister company Circle Line Downtown run everything from the 20-minute Ikea Express ferry between Wall Street/Pier 11 and Red Hook (free on weekends, $5 for anyone over age 5 on weekdays) to tours that include all-day ferry and bus passes and even a combination cruise and helicopter ride around the Statue of Liberty. Â You can hop between locations in Manhattan and Brooklyn or opt for a traditional narrated tour.
The Liberty Landing Ferry goes between the Liberty Landing Marina and Warren Street terminals in Jersey City, and the World Financial Center Terminal in Manhattan, connecting Wall Street and the 9/11 Memorial and Museum with Liberty State Park, where you can play, picnic, bike, visit the Liberty Science Center and even go on a kayak eco tour, if your kids are at least 16. And of course, there’s the grandmommy of them all, the Staten Island Ferry.  It’s got killer views, you can buy a snack, and it’s always free.