What's the Liberty Bell?" asks six-year-old Caroline.

"Do we have to wait?" asks nine-year-old and more-to-the-point Tabitha.

I start to say yes, because every whirlwind Sunday tour of Philadelphia ought to start with the famous cracked bell, but I experience a sudden deja vu. I'm a kid again and we have driven for hours to see Plymouth Rock and there it is -- an anticlimax enshrined in an iron cage.

"No, I guess we don't have to," I say, and we leave the line in the crowded pavilion where the Liberty Bell rests. With that great weight of bronze lifted from their chests, the children literally skip the block and a half down Market Street to FRANKLIN COURT, where the city's other famous symbol lived, printed and sold stamps.

"Which year do you like best?" one child asks another, pointing to a display of dolls dressed in letter-carriers' uniforms of the past 200 years or so. When the year 1873 is chosen, a postal clerk, dressed in the knee breeches, vest and loose blouse of the year 1775, looks up from his stamps and says, "Ah, yes, that was a good year."

There's a postal museum upstairs, but the children exit through the back door into an attractive garden with a steel skeleton showing the house that Ben Franklin built for his family. The rental house he built for investment is still standing and used as an archeological exhibit.

"Look at all the broken things!" says Caroline, taking in glued-together pitchers, blue-and-white china, tumblers and chamber pots, some in situ, others in glass cases.

In Franklin's print shop, a woman in an 18th-century gingham dress is using inkballs made of leather covered with wool to spread ink over some type. The result -- four pages of a book of Franklin's sayings entitled "The Way to Wealth" -- is then hung up to dry. Other works printed here are for sale, including the Declaration of Independence.

"Where did they sign?" asks Tabitha, considering a purchase.

"Actually, it was printed a month before they all signed it," explains the printer. "They didn't sign it until August 2."

Convinced, we roll up our purchase and head down a ramp to an underground museum filled with Franklin inventions and memorabilia. Midway, we pass through a mirror-lined room with neon signs proclaiming Franklin's talents as inventor, statesman, etc.

"This must be Benjamin Franklin's disco," says Tabitha. But the best is yet to come: It's a room filled with telephones and posted with the phone numbers of people from George Washington to D. H. Lawrence to Harry S. Truman, all of whom have something to say about Franklin.

"Mommy, I just talked to George Washington!" says Caroline.

I was more interested in what Balzac had to say, though he was uncharacteristically polite and merely thanked Franklin for the lightning rod and the republic in that order. After an excellent, 20-minute movie about Franklin, we emerged into the light again and wandered among the 18th-century gardens and buildings, popping into CARPENTERS HALL, where the First Continental Congress met in 1774, and ending up at the City Tavern.

"That looks like the stove he invented," said Caroline, pointing to a Franklin stove in the rebuilt hostelry where we ate a lunch of roast beef sandwiches.

Pleased, I pushed luck: "When they were meeting for the Continental Congress in that building we were just in..."

"They came here for Bloody Marys," finished Tabitha, reaping, for her smart-alecky ways, a long discourse on Mary Tudor.

As a change of pace from people in knee breeches, we headed for the PHILADEPHIA ZOO, billed as America's first.

"Coming up on my right is a dromedary camel," explained the guide on the safari monorail that wound around and above the zoo and gave us a feeling of being right in there with the animals. Below us, on the African Plains, a giraffe chased an ostrich. In Bear Country, one playful polar bear pushed another off, a cliff and into a pool, then jumped in himself, to the delight of spectators at an underwater window. In the Children's Zoo -- an extra 50 cents in addition to the admission price of $3.50 for adults, $2.50 for children -- you can pet the goats, feed the sheep and, for another 75 cents, ride a pony.

Having hoofed it to the zoo from the Philadelphia Museum of Art -- a pleasant but rather long walk past the boathouses along the Schuylkill River -- we headed back into town on a trolley, almost as much of a novelty for the children as the monorail. Transfering to a No. 48 bus, we soon reached our next don't-miss-it destination, the FRANKLIN INSTITUTE, which is not so much a museum as a collection of experiences -- such as boarding a Boeing 707 or walking through a human heart.

"You are now leaving the heart and entering the lungs," says a road sign as you wind your way through the thumping pink, white and purple multi-story facsimile, then press buttons to make facsimile blood flow through veins clogged with cholesterol.

In an exhibit on naval architecture, kids are building ducks according to a naval architect's plan, and, in a related exercise, comparing types of ships to see how much cargo they can stack on the deck of a ship before it sinks or capsizes. In an exhibit on mechanics, kids dangle from ropes attached to a lever while other kids try to lift them. Blocks are stacked and one block is knocked from under them to illustrate the principle of inertia, while marbles are dropped from a tower to illustrate gravity. When her eyeballs have stopped bouncing to follow the marbles, Caroline moves to the sand pendulum, then tries to balance a wheel by changing the position of brass pegs. Tabitha, meanwhile, is involved in a tug-of-war to illustrate the idea of drag.

Reluctantly, I drag them away to a room filled with mirrors -- mirrors that turn kids into coneheads, cylindrical mirrors that make sense out of nonsense pictures, even mirrors that form a whisper chamber.

"This is fun," whispers Caroline into a ring tied to a string in front of a convex mirror on one side of the room.

"It works!" yells Tabitha, getting her message through a similar ring on the other side of the room.

If kids aren't turned on enough, there's a demonstration of electricity where young volunteers from the audience are turned on literally with the aid of a van der Graf machine.

"Where's a good place? Where's your appendix?" asks a demonstrator, sticking a fluorescent light bulb into that area of the anatomy of a nervous looking boy, then using the electricity in the hair of a girl to light an incandescent light bulb.

Leaving Tabitha playing games with a computer, Caroline and I walk a few blocks to the PLEASE TOUCH MUSEUM, designed especially for three-to seven-year-olds. Here, as at the Franklin Institute, there are so many attractions we are torn in several directions. Shall we pat the bunny or fondle the guinea pig; try on a wedding gown cut down to child size or rubber-stamp papers in "the office"? Then there are Japanese kimonos and shoes to try on, a construction site and a medical center. Caroline fits a cast over her leg, then tries walking on crutches. Another child is putting on a puppet show in the puppet theater, and friendships are being struck in the supermarket.

"Hello, what are you doing? I'm shopping, too," says a girl filling her basket with plastic pineapples and oranges.

"I didn't really have time to play," complains Caroline as the museum prepares to close.

We headed for PENN'S LANDING, a floating museum on the Delaware River consisting of six ships, from schooners to submarines. Realizing we didn't have time to see them all, we went straight for the Moshulu, which is a restaurant as well as a museum. The largest steel sailing ship in the world when she was built in 1904 to shuttle nitrate from Chile to Europe, the Moshulu won the last great grain race from Australia to Europe before World War II was over, ending her commercial-sailing days. After exploring the decks, peeking into the galley and the cabins, we settled down for supper. As we watched the moon rise over New Jersey, the waiter brought us bread and some butter stamped with the shape of a bell.

"There's that bell again," said Caroline.

The Liberty Bell had left an impression, after all.