Updated

The city's glitziest, most star-studded parades of the Carnival season roll this weekend, including one with a float being touted as the biggest in New Orleans' history.

Mardi Gras is Tuesday, but more than a dozen parades roll in the days leading up to Fat Tuesday. The big ones that feature celebrity float riders include Endymion, Orpheus, Bacchus and the all-women Krewe of Muses. Dozens of others will roll elsewhere in Louisiana and along the Gulf Coast in Mississippi and Alabama.

While Endymion boasts that it will have the biggest float the city's Carnival has ever seen, the Bacchus parade is shaping up to be a larger-than-life experience for more than two dozen child cancer patients from seven hospitals across the country.

Bacchus is providing costumes and throws -- trinkets for tossing to the crowds -- to 28 teens and pre-teens being treated for cancer. They'll ride in Sunday's parade with this year's celebrity king, actor G.W. Bailey, co-star of the TNT show "Major Crimes."

Bailey, 68, is known for his roles in the "Police Academy" movies and the cable TV crime drama "The Closer." He also serves as executive director of the Sunshine Kids, a nonprofit that takes patients on trips to major U.S. cities. It regularly takes kids to New Orleans during Carnival, but not usually during the season's big weekend.

Bailey said the trips give patients a break from treatments and the opportunity to spend time with teenagers going through similar experiences.

"When you're a teenager, the worst possible thing that can happen to you is isolation," he said. "Even if you're in a room full of people, if you're not with another teenager losing their hair, going through what you're going through, you feel alone. We bring those kids together. We give them a common experience, and within two days, the wigs come off and they don't have to worry about their scars, their missing limbs. It just doesn't matter anymore."

Bailey and Sunshine patients arrived in New Orleans on Tuesday to a packed weeklong schedule that includes eating in some of the city's finest restaurants, taking a south Louisiana swamp tour, and visiting the Audubon Zoo and Aquarium of the Americas.

But the trip's highlight will be Sunday's parade, said 17-year-old Paden Blevins who is in remission after two bouts with Hodgkin's lymphoma.

"I'm so excited," she said. "When they told me I was going to be riding in the parade, I was like, are you kidding me?"

Bailey also will visit patients at Children's Hospital in New Orleans on Friday. It's a tradition held by previous Bacchus kings, including Saints quarterback Drew Brees and actors Will Ferrell, James Gandolfini and Kirk Douglas.

Bailey and the patients also plan to watch Saturday night's Endymion parade, led by pop star Kelly Clarkson. Clarkson, the first winner of TV's "American Idol," is scheduled to perform after the parade at Endymion's ball at the Superdome.

The parade's other star is the "super float" that organizers bill as the largest and most elaborate in Carnival history. Parade floats typically reach lengths of about 50 feet (15 meters) and can carry about 40 riders, but this one will be 330 feet (100 meters) long and carry more than 200 people.

The float's design is a tribute to Pontchartrain Beach, the amusement park that entertained generations on the New Orleans lakefront before closing in 1983. The float will include a moving replica of a roller coaster, cotton candy and popcorn machines, and pictures and videos of the old amusement park.

The float will be divided into sections so it can make turns on New Orleans streets. After its Endymion debut, it will be on public display at Mardi Gras World, the huge studio and warehouse where Carnival floats are made.

The big weekend was set to kick off Thursday night with the Muses parade and its celebrity rider, Civil Rights icon Ruby Bridges. Bridges, who ended segregation in New Orleans public schools in 1960 by enrolling at a previously all-white elementary school at age 6, was to ride aboard the krewe's signature float, a brightly lit red high-heeled shoe.

On Monday, actor Gary Sinise and New Orleans musicians Troy "Trombone Shorty" Andrews and Harry Connick Jr. will ride in the Krewe of Orpheus parade. Joining them will be Emmy- and Golden Globe-winning actress Mariska Hargitay, the Imagination Movers family-friendly rock band, and Animal Planet's Tillman, the skateboarding bulldog.

Carnival season culminates Tuesday with the pageantry of the Rex and Zulu parades and as many as 1 million people reveling in the streets.

The celebration follows the American football championship Super Bowl weekend, with sold-out hotels, some 150,000 visitors and $432 million in economic impact, said Kelly Schulz, spokeswoman for the New Orleans Metropolitan Convention and Visitors Bureau.

Hotels are near capacity for this weekend, "but there's still some availability," Schulz said. "The hotels aren't as booked as they were for Super Bowl, but they're very full, so that's a good sign that it's going to be a very successful Mardi Gras."