One hundred people RSVP’d for William’s sixth birthday party, which was held at a Los Angeles park on a March afternoon. By 12:30 p.m., the fire station-themed event was in full swing, with energetic attendees trying on their own fire-hose backpacks and gleefully coasting down slides into a large custom ball pit, detailed with flames and the slogan “Let’s Get Fired Up.”

Preparation for the event had begun three months before when Sabrina Maldonado and Melissa Mueller of Stay Golden Design began working with William’s mother and 14 vendors to hammer out all the details.

The morning of the party, the planners installed a 20-foot-wide wooden backdrop that looked so convincingly like a fire station that a child attempted to open a one-dimensional acrylic door. With permits from the city, they blocked off street parking for guests and a food truck, and propped up more than 40 feet of balloon garlands. Guests sat under canvas umbrellas at long wooden tables, painting ceramic fire trucks. (A real-life fire truck eventually made an appearance, fresh from a party in Brentwood.) There was a beverage station with customized drink stirrers and signature to-go cocktails for the parents, including one called “What the Fire Truck.”

The birthday boy, who was periodically trailed by a photographer and videographer, stood next to his mother, eating water ice (a frozen dessert) from a vendor’s cart. He said he didn’t know what his favorite aspect of the party was, but his mother, Katie Provinziano, 39, suggested that it could be the water ice. “I was the first customer,” William said proudly.

If not all of the specifics were appreciated by the children, they were certainly clocked by the adults.

“The details never cease to amaze me,” said Maisie Pacia, a parent in her 30s who was snapping photos of it all. She’d come with her husband, Rich Radford, 49, and their 4-year-old daughter Harlow.

Mr. Radford mentioned that the level of production was actually dialed back from William’s fifth birthday party, which was hibachi-themed and featured real chefs and pyrotechnics. “For instance, there are no fire dancers today,” he said.

Aga Green, 40, who was waiting in line for the food truck, said that about half the birthday parties she attends with her children had a similar level of flair. ”I feel like people celebrate their children more than they celebrate themselves.” Mila, Ms. Green’s 6-year-old daughter, ran by holding a plush toy from the Adopt Your Own Dalmatian station. (“Friends!” Mila said, of what she was enjoying most.)

William’s birthday party represented a level of production that has become increasingly common among a subset of Angelenos throwing birthday parties for their children. Or, more often, hiring professionals to throw those parties.

Instead of a table at a paint-your-own pottery place or a bounce castle in the backyard, the level of décor and amount of planning involved in a young child’s celebration can rival a wedding.

“It used to be that over-the-top was looked down upon, but now over-the-top is applauded,” said Leesa Zelken, the founder of Send in the Clowns, a party-planning service in Los Angeles.

Ms. Zelken started her business 30 years ago, when she supplemented her income as an actor by dressing as a clown at children’s birthday parties. (She still remembers grandparents of a birthday boy balking at the extravagance.) In 2005, during the reign of the cupcake, she expanded to tablescape and decorating services, which these days seems quaint.

Every event Ms. Zelken now orchestrates includes multiple vendors. Her consulting fees start at $350, and soup-to-nuts planning packages begin at $14,500. “For an event that I just booked, we’re doing furniture rentals, a performer, a glitter tattoo station, a craft station, a pancake artist, a party manager and a lifeguard — because there’s a pool and we need to make sure no one falls in,” she said. “That’s a very midsize party.”

The ratcheting-up of expectations may have something to do with the pandemic. Parents were pent up for two years and emerged wanting to go big for their children’s milestones.

Then, of course, there’s Instagram. “Social media’s just doing the job of the school gossip,” said Joshua Castillo, a parenting consultant in Los Angeles. “There’s always been social media, it just used to be a person who found out how much something cost, maybe took a picture, and showed you the goody bag from the party.”

And it’s impossible to ignore the influence of the Kardashians, whose events introduced new standards for what it means to celebrate. “Around the time Kim had a party for her first child, and it was something that was featured in People Magazine, something shifted,” Ms. Zelken said. (“KidChella,” as that party was called, featured a Ferris wheel and an ill-advised American Indian headdress). “People had this drive to get to that same level, or close to it.”.

“So much of my Instagram feed is parties,” said Ellina Chulpaeff, a 31-year-old attorney. For her son’s first birthday, which she combined with a birthday celebration for herself, she executed an Italian theme. There were tablescapes accented with lemons and blue-and-white Italian-style ceramics, and a faux boxwood wall backdrop.

“When I see stuff on Instagram, like insane parties in Beverly Park, or Mindy Weiss caliber,” she said, referencing the Kardashian family’s event planner, “I grab those ideas and vendors.”

She isn’t the only one. MESH, a company known for its customized ball pits, has had so much success since its first brush with the Kardashians (Kim and Kourtney) that it had to hire a mechanical engineer to develop a color sorting technology for the 40,000 balls it uses every weekend. And after Jme and Moi Andrade of Balloon and Paper, a balloon artistry company, created an Instagram-breaking balloon tunnel in custom shades of brown for a baby shower thrown by Khloe Kardashian — or “Khloe,” as Ms. Andrade calls her; even those in the industry who haven’t worked for them tend to use first names for Kardashians — 70 percent of their company’s business has been children’s parties.

Parties for the uber-wealthy can clock in at $75,000 or more (some families don’t have budgets, Ms. Zelken said), but other parents who hire professional planners might spend between $10,000 and $40,000.

Ms. Chulpaeff estimated that her son’s Italian-themed birthday, which she planned herself, cost $16,000. She has never regretted the expense. “Every time I look back at the pictures I smile,” she said.

Ms. Chulpaeff grew up in Los Angeles, but even the big to-dos within her Russian Jewish community didn’t match what she sees at parties now. “A lot of people were baited into it the same way I was, where you have all of these produced parties related to your wedding, and it sets a new standard.”

From there, she said, it was a Pandora’s box. “You can’t imagine a party where there isn’t catering or a professional photographer or a pretty backdrop so everyone can share it on Instagram.”

Ms. Zelken said that before the pandemic, a certain perfectionism drove mothers. “Moms wanted to do it all,” she said. “They wanted to have the best house, school, throw the best parties. They didn’t want someone else to throw it for them or for it to look like someone did. But during Covid, parents had way too much on their plate. Now it’s OK for them to say, ‘I can’t do this.’”

One thing that hasn’t changed, both planners and parents agree, is celebrating a child’s interest — “Frozen,” sushi, waste management, mermaids — with a theme.

(Or it may be a parent’s wish for what the child’s interest could become. Frannie Hudson, an in-demand planner, threw a Ruth Bader Ginsberg-themed party for a 1-year-old in which she put doilies under balloons to mimic the justice’s iconic collar).

Party professionals also emphasize that parents typically want the party to feature a signature visual note, Ms. Mueller said. “Everyone wants that Instagrammable moment.”

And those moments are, according to Ms. Castillo, eventually noticed by children, whom she said can start to request features they observe at other parties as early as 5 years old.

“They start to say, ‘I’m going to ask my mommy for a jumpy house, I want a magician, too,’” she said. “They’re boutique shopping — suddenly they see what’s available. Those kids very quickly learn, ‘These are status symbols that I have to have.’”

Ms. Castillo, who has worked with families of all income levels and is the author of “Surviving Children’s Birthday Parties: How Moms and Dads Can Stay Sane and Still Give Their Young Children Happy Birthdays,” notes that she often observes stress or an outright lack of joy among parents planning birthday parties. These celebrations can be great for fostering community, she said, but are also viewed by some families as networking events.

“There’s almost this awkward social contract that parents think they’ve signed onto within the group they’re surrounded by,” Ms. Castillo said. “It seems like they feel pressure.”

Bridget London, 41, recently brought in a temporary tattoo station, a face painter, a light-up dance floor and Milo the Unicorn (an Azteca horse accessorized with a colorful mane and horn) for her daughter’s fifth birthday. “LA is just different,” she said.

Ms. London noted that many schools require the entire class to be invited to a party, which means they tend to get big quickly.

But there may be something else about the city, too. “I think a lot of people want to make magic for their kids,” Ms. London said. “Los Angeles is a place where people come to make fantasies happen, right? Everyone is kind of a fantastical thinker.”