Isaiah Thomas booked his first modeling job at 11 days old, three days before he was legally able to work. At 3 months, he was eligible for a Screen Actors Guild (SAG) card.

Casting agents couldn't get enough of his goofy, gaping smile and round, symmetrical face. He booked Target. He booked J.C. Penney. He booked the Disney Store. He even booked an Enterprise Rent-a-Car commercial.

But then he hit 13 months and it all came crashing down. When the photographer at an Old Navy audition last spring approached to take some test shots, Isaiah screamed, throwing his head back and stomping his feet on the ground.

Now he's probably unemployable until he's 3 years old, if he's even still cute then. Washed up before he can even wash himself.

L.A. can be a brutal place for those trying to turn their looks into fame and fortune, but no group of performers has so short a shelf life as babies. Most productions prefer babies who can sit up but can't crawl away, meaning they typically need to be between 6 and 9 months old.

Only the Karlie Klosses of the infant set can sustain a career for as many months as Isaiah did. Then you hit the Terrible 2s, that notorious phase of aggressive limit-testing, which often begins shortly after your first birthday. Most of the work dries up until you grow into your size-3T overalls.

Unlike the scam artists who charge $1,000 for headshots, the 20 or so L.A.-based talent agencies that place babies and toddlers in major films and ad campaigns don't advertise. Smart moms email snapshots directly to the heavyweights at the Osbrink Agency, Zuri Model and Talent, L.A. Models and Paloma Model and Talent, which represents Isaiah and his older brother, Imari Jr., who turned 3 in September.

The cutest, most mild-mannered babies can make bank from the cradle, earning $1,000 for a day's work, plus residuals. But enterprising parents need to act fast to take advantage of that. Unless, of course, the kid starts making more than $1,800 per quarter.

Because then your tantrum-prone toddler can file for unemployment benefits.

Every day, Paloma Jackson receives 75 to 100 snapshots from parents who believe their child is the most precious and adorable creature in the world. She might accept one or two as clients.

Siblings of working models have the best chance. “We don't believe in telling a family your fourth kid's cute and your other three aren't,” Jackson, 39, admits. As a result, her agency represents about 1,250 children, including many siblings, but only about 750 kids get regular work.

A no-nonsense workaholic, Jackson booked all six babies who shared the part of baby Tyler in The Hangover. She also booked 6-year-old Grant Holmquist, who, as a baby, shared the part with his twin sister in The Hangover Part II and took over as toddler Tyler in The Hangover Part III. (Ninety-five percent of jobs for TV and film are booked by “multiples,” meaning twins or triplets, because child labor laws limit the amount of time kids can be in front of the camera.) At Part III's L.A. premiere in May, Holmquist walked the red carpet with celebs like Zach Galifianakis, whom he calls “Zachy.”

When we think of stage moms, we tend to think of frantic women plying coiffed and mascara'd daughters with go-go juice, and Jackson certainly has seen her fair share of competitive shenanigans on-set. One mom might try to make another baby cry so that her kid, the understudy, gets on camera. Another will generously put out brand-new toys for all the children at an audition, only to put them away a few minutes before the others go in, maximizing the chance of tears. Always pack a surprise Barbie, Jackson recommends, to cope with this trick.

Isaiah's mother, Tatiana Thomas, 24, is trying to challenge these stereotypes and help parents navigate the industry with StageMomz, a consulting company she started last year. In addition to working full-time as a legal assistant during the day and finishing her degree at Loyola Marymount University at night, Thomas counsels parents and will submit photos to her contacts at five agencies for a paltry $30. If you'd prefer to post a profile on the L.A. Casting website without using an agent, she'll even get you a discount with a professional photographer such as Shea Anne, 26, a former model who knows to shoot in natural light, blow bubbles to make her subject smile and avoid stripes, logos and pastels.

Thomas also offers modestly priced guidance: Get work permits for free online. Bring snacks, diapers, wipes, toys and a binder of all your paperwork to every audition or job. Open a Coogan bank account, where 15 percent of your child's income must remain by law until he hits 18. If your baby is teething or grumpy, don't take him to an audition. And unless you're desperate, avoid open casting calls, where you can wait for hours upon end in a sweaty hallway filled with scattered Legos, nursing mothers and screaming babies.

But the competition doesn't end once parents have secured an agent for their child. Desperately looking for access to the most lucrative, high-profile jobs, parents often turn to the private Facebook pages of leading agencies, where advice, taunts and humblebrags mix with announcements about upcoming auditions. All across Southern California, apparently, moms and dads click through galleries of success stories, seething, and ask: Why didn't my baby get that job?

Thomas says she does her best to stay out of the Facebook drama. As she waits for Isaiah to pass through his unruly phase, she's focusing her energies on StageMomz and on her older child, Imari, who is finally big enough to ride the wave of jobs for 3- and 4-year-olds.

Two years ago, Imari was the one on top, shilling for Wal-Mart and stealing scenes in music videos for will.i.am and Britney Spears. In fact, it was Imari's success that helped Isaiah get a bootie in the door when he was still in the hospital.

But a few months ago, a trip to the barbershop left Imari with a defined hairline, like an adult's. Thomas hadn't really noticed the difference, but Jackson was appalled. In order for Imari to get any more work, she says, he needed a more childlike haircut. Before Imari could dazzle at his Nike audition earlier this month, mom and model had to wait for the 3-year-old's hair to grow out.

Encouraging parents to accept a casting agent's idea of what makes for an attractive baby sometimes can be difficult. Kathy Bolde, who runs the baby/toddler division at Zuri, insists that every baby really is cute, just as every mother believes, and that it's really what's on the inside that counts.

“It takes kind of thick skin sometimes to be in this industry, because parents need to remember that looks aren't truly what matters,” Bolde says.

“But unfortunately,” she continues, “in modeling, it does have to do with looks.”

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