The children and parents awoke Sunday in homeless shelters around Greater Boston and boarded school buses, some with no idea where they were going other than to a Christmas event.

As they entered the Boston Convention and Exhibition Center, solemn faces broke into wide smiles and dropped jaws as they stepped onto a red carpet toward people waving and applauding them, along with extravagantly costumed characters — Disney princesses and Superman, Star Wars storm troopers and the Incredibles — all there to welcome them. Snowflake confetti fluttered. Lights sparkled. Parents dance-walked to the upbeat Christmas tunes, filming their children’s faces on phones, some with tears in their eyes.

“Wow, it’s beautiful!” said Aylajoy Dufresne, 5, who wore a pink tutu, as she ran to princess Elena of Avalor and hugged her. “Elena!”

“I wasn’t expecting all this,” said her mother, Cassy Dufresne. “I’m very grateful to be here; this is getting us in the Christmas spirit.”

Thousands of volunteers rallied this year to serve more than 6,000 people from dozens of shelters at the 31st annual Christmas in the City, which has grown from a small gathering at City Hall in 1989 to a massive party thrown for families struggling with homelessness.

The event featured performances by the Blue Man Group, a gospel choir, and an Afro-Caribbean band, as well as a petting zoo, amusement rides, Santa Claus photo booths, face paint, manicures, haircuts, dental screenings, flu shots, and white-clothed tables holding pizza, chicken tenders, and gingerbread cookies.

This year took on particular poignancy because the founder and lead organizer, Jake Kennedy, 64, has been diagnosed with ALS, which took the lives of his father and brother. Kennedy’s son, Zack, a neuroscientist at University of Massachusetts Medical School, has dedicated himself to researching a cure for the lethal disease. Amyotrophic lateral sclerosis, also known as Lou Gehrig’s disease, is a progressive and eventually fatal neurological disease in which a person’s mind remains strong while the body slowly loses its functions.

“This is a big year,” said Alexandra Lee, who has helped manage the event’s volunteers for 25 years. “We’re here to support him and make sure Christmas in the City stays as wonderful as it’s always been, and to support the family to fight this.”

Mayor Martin J. Walsh of Boston stood onstage beside Kennedy and his wife, Sparky, and expressed his gratitude and admiration of Jake Kennedy.

“Many of you in this room might not know him personally, but he does this because he loves you,” Walsh said. “He loves every single family in our Commonwealth, in our country. . . . He is my hero.”

Kennedy raised his arm to the applause that broke out, his face serious as he looked at the crowd before hugging Walsh.

Offstage, Kennedy struggled to speak, though he made a point to say one thing.

“When you ask people what they like best — the winter wonderland, Santa, the food, the Blue Man Group — they all reply, ‘This is the first time in our lives we’ve been treated with dignity and compassion,’ ” Kennedy said. “That’s because of the volunteers.”

His wife added: “We all deserve to be treated with dignity and compassion.”

Many parents said they were thrilled to see their children laughing and having fun with activities they can rarely access.

“I don’t want to miss anything; this is beautiful,” said Anthony Raye, as he and his son, Antonio, 10, plotted their next moves: face-painting and visiting animals.

“I just want to have fun and take care of my dad,” Antonio said.

Along one wall, children were petting therapy dogs, whose tails wagged. “Nice doggie!” a girl said, as she stroked a golden retriever named Rider.

By a “salon” sign, hairstylists buzzed, cut, and blow-dried the hair of parents and kids.

Aaron Lauderdale, 7, received a mohawk, his face painted like a green Grinch.

“This is the one and only time I’ll let him have a mohawk,” said his mother, Natashia Lauderdale. “This is his day. I’m just along for the ride. I feel like a big little kid all over again.”

A parade led by men playing bagpipes filed through the room, followed by Santa Claus on a raised platform. The Kennedys led a countdown, prompting a red curtain to rise on one wall, leading to a winter wonderland of amusement rides and a petting zoo. Children clamored for a carousel, flying chair swings, bouncy castles, super slides, trampolines, and a rock-climbing wall.

Michaela Singletary took photos of her 2-month-old son and marveled at the sheep, parrots, and camels. Kids nearby fed goats and petted a tortoise.

“I’m trying to make memorable things so when he gets older, he can look back and see, ‘Wow, my first Christmas was special,’ ” she said.

Amelia McCauley pushed her 2-year-old, Lauryal, in a stroller.

“I feel special,” she said. “I don’t know when something like this is going to come by again, so I just want to enjoy it.”