"They don't let you climb on the cannons here!" the six-year-old griped.

"Yeah - but at least you can see what they've got," replied the sophisticated eleven-year-old.

We had just discovered the new Marine Corps Museum at the Washington Navy Yard, and the boys were comparing it to the cavernous old Navy Memorial Museum down the block that had long been a favorite of theirs. We all agreed that the Navy Museum was somewhat like Grandma's attic (if Grandma's attic were the length of a football field) - a huge collection of unrelated items all thrown together in a comfortable but confusing jumble - while the Marine Corps Museum was more like a small modern house - beautifully designed but formal, with clean, spare lines and no wasted space. The collection it houses was moved up from Quantico last year.

The new museum is like the Marine Corps itself. With patriotic march music the Corps band pipes you into the 19th-century building, which served as a barracks until 1975. Exhibit signs are bordered in red, the original walls are white and new walls and carpets are blue. There is no confusion about which way to go. Clearly written labels lead you down well-lit halls.

First, a collection of lightweight landing guns and machine guns, 19th-century to modern. Then the time tunnel, summarizing 200 years of Marine Corps history. You are informed that this display is broken up into 20 consecutive segments, each representing an important era. There's no question about organizator: Exhibits on the left show three-dimensional objects (uniforms, weapons, equipment) while those on the right highlight personalities of each period through photographs, letters and reports. Both sides are full of fascinating memorabilia. On the right in the Civil War segment, a handwritten account of Lincoln's famous address by a lieutenant who traveled to Gettysburg with the Marine Band. On the left in the World War II sector, General Lemuel C. Shepherd's "short-snorter," a string of paper bills taped together, each a souvenir of an area he visited, autographed by his buddies. The dollar that started the string was supposed to be reserved by the owner for his first short snort when he got home. On the right, photographs of 1920s Marines in hot pursuit of bandits in Nicaragua. On the left, tokens from the liberation of the Mayaguez off Cambodia in 1975. On the right . . . go and see for yourself. The time tunnel gives a brief rundown of every major Corps action from the Revolutionary War to Vietnam, so that an older child can quickly get a clear overview of American military history.

Out of the tunnel and into combat art, an often-overlooked aesthetic sub-specialty.Sculpture, paintings, photographs and drawings capture the real feelings of men in combat - fear, cold, loneliness - a far cry from the televised heroics that children usually see. Of special interest is the famous 1945 photograph of "Flag Raising on Suribachi," which provided the model for the Iwo Jima memorial, and the story behind the picture.

Another gallery, reserved for changing exhibits, now features an amusing array of recruiting posters, past and present, and a small but select gift shop completes the tour. The museum also has a fine collection of John Philip Sousa's music plus library and research facilities.

Because the exhibits require a fair amount of reading and because of the "do not touch" atmosphere, the six-year-old and the eleven-year-old concluded that the Marine Corps Museum was more interesting to older children, while the Navy Museum, with its movable guns, operable periscopes and climbable ship decks, was more fun for younger ones.

Both museums are part of the Navy Yard's effort to create a "Historic Precinct" through the restoration of several Victorian-era buildings. Brochures and a 12-minute slide show at the visitors center in the old commandant's office will familiarize you with what's open now and what's yet to come. If you take your family to the Navy Yard, plan to spend a whole afternoon, because there's lots to see. Call ahead to find out if any ships will be docked, as visiting ships are often open to the public and kids love to tour them. The Navy Yard is off the beaten tourist track, so the museums are usually empty.

There's ample parking in various locations and, best of all, everything is free.