The favorite indoor mecca for families — it drew almost half a million people last year according to museum officials — will not charge for the Great Hall. Thousands of area babies can still learn to walk for free in that carpeted, air-conditioned toddler pasture. But it will now cost $3 a head to get into the popular Building Zone kids area.

The Museum will also charge for exhibits — $8 for adults and $5 for children under 17, students and seniors. The LEGO Architecture exhibit, which had charged for admission, proved that families are willing to pay for worthwhile exhibits. It drew 136,000 people between its July 2010 opening and this May. It’s been extended until September 2.

Military personnel and their families are free until Labor Day.

The Museum’s three annual family festivals will remain free of charge: Discover Engineering Family Day in February, the National Cherry Blossom Family Festival in March, and the Big Build on September 17th.

“It is time to reexamine how we maintain our mission and our commitment to the public good, and to discover new resources, new practices, and even new skills that enable us to become a thriving museum for the future,” said the museum’s executive director Chase W. Rynd in a statement.

My colleague Jacqueline Trescott reported that the Building Museum’s managers made the change because of loss of revenue, including a cut in Congressional funding. The building museum had received $369,000 in 2010 but was reduced to $105,000 in fiscal 2011.