A proposed view of the ‘World Cultures’ area of the National Children's Museum's Our World gallery. (Courtesy National Children's Museum)

Willard Whitson, president of the National Children’s Museum returns a phone call instantly, then makes a joke of it. “We promise a quick turnaround on everything but museums,” he laughs.

The question of when the former Capital Children’s Museum, which closed its Washington location eight years ago, would reopen has been a running joke, Whitson says. “Although we stopped laughing several years ago.”

The answer was just announced: Dec. 14 at National Harbor, in a new 18,000-square-foot space.

When the museum closed, it was scheduled to reopen as the National Children’s Museum within four years. But the developer of the L’Enfant Plaza location scaled back his initial plans, and the space no longer worked.

The museum operated as a “museum without walls,” doing school and community outreach and partnering in the White House Easter Egg roll, while looking for new space. It is moving its offices from L’Enfant Plaza to National Harbor this month.

Whitson says the fastest-growing type of museums in the country is for children. What “we do especially is create opportunities to learn through play,” he says. We “are a collection of learning experiences. . . .We are committed to the fact that play is the ‘work’ of childhood. It is a necessary component for the healthy growth of an individual.”

The “Our World” portion of the museum will have a three-wheel “tuk-tuk” from Thailand that kids can pretend to drive and will show them how people in some countries get around. In the “3 & Under” gallery, “ we’re the home of the Sesame Workshop.”

The new joke for parents who have watched kids grow while waiting for the Children’s Museum to open: You might want to have a new baby, just to take him or her to the Sesame Workshop. Whitson likes that one much better.

National Children’s Museum

opens Dec. 14 at 151 St. George Blvd.,

National Harbor.