From PEOPLE Magazine Click to enlarge
As any new parent knows, there is only one certainty when it comes to life with a baby: Things rarely go according to plan. So when the day arrived for 3-month-old Prince George to be christened into the Church of England, his mom and dad hoped for the best. Arriving at the Chapel Royal in St. James's Palace in London on Oct. 23, Prince William shared that it was the first time his son had been quiet all day. "He's all ready," William told the small group of family, including his grandmother Queen Elizabeth, his father, Prince Charles, and his brother Prince Harry. "So far, so good." For the duration of the 35-minute ceremony - during which the Archbishop of Canterbury splashed water from the River Jordan on George's head three times and instructed his parents to help their firstborn "grow and flourish" - George "was fairly calm; no screaming," says a royal source. "I don't think he had a 'moment' at all." The prince was so docile that even his mother expressed her relief the next evening at a charity gala she attended at Kensington Palace, while a "fast asleep" George remained in his dad's care for a few hours. "He was such a good boy," Princess Kate, in a V-neck dress by Jenny Packham, told guests at the event sponsored by 100 Women in Hedge Funds, which supports various charities. "We're very lucky. He's not always like that!"

Still, having rounded the 100-day milestone after his arrival on July 22, the chubby-cheeked prince is already proving himself a natural at hitting his royal marks. Making his first public appearance since William and Kate, both 31, carried him out of St. Mary's Hospital on July 23, George gurgled happily for a series of historic christening day portraits - even striking a sweet smile while gazing up at his adoring mom. If the newest heir to the throne isn't always quite so easygoing - his grandma Carole Middleton "did say that he has a nice pair of bellows on him; a good set of lungs!" Middleton family friend Martin Fidler tells PEOPLE - he had no trouble charming the millions of fans around the world, who delighted in everything from his hand-sewn lace christening gown to his family's obvious joy. Attending the Oct. 24 gala, Kate "said he is a wonderful baby, and they are having a lot of fun with him," says Mimi Drake of 100 Women in Hedge Funds. "She was as excited about Prince George as any new mum would be."

With the young family's first major milestone behind them, William and Kate can focus on finding their way as new parents and enjoying their son's emerging personality. Having survived the "fourth trimester" - lots of crying, little sleep - they are now entering the happy baby stage as they settle into their new home in Kensington Palace. Since moving into the newly renovated 20-plus room "apartment 1A" in early October, Kate has continued to rely on help from both nanny Jessie Webb and housekeeper Antonella Fresolone. The recently renovated upstairs nursery "will be the centerpiece of life," says former royal bodyguard Ken Wharfe, who served Princess Diana when William and Harry were young boys. "For [much of] the next year, George will be quietly upstairs."

As for life with a newborn in Kensington Palace, just because the future king might be napping doesn't mean the rest of the household is in whisper mode. "The nursery is out of the way, so William and Kate can have a dinner party or have the Queen for dinner downstairs, and nobody would hear a thing," says former royal chef Darren McGrady. "There's no tiptoeing." Nor does the royal family typically curtail their favorite pastimes with the addition of an infant. "I held Harry as a baby at Balmoral," says McGrady, "and I remember [having a newborn there] didn't stop them from shooting every Thursday and Friday, guns going off. It's the royal family - you carry on."

While both new parents are determined to be as hands-on as possible, they are also constrained by the requirements of duty. "They can't be stay-at-home parents," says Ingrid Seward, author of Majesty magazine's book A Century of Royal Children. "They have to be out doing things. Kate can't lug her baby everywhere with her. So it is restricted, however normal they want George's life to be." George is clearly bonded with his parents, who "are obviously very astute to his needs," says maternity nurse Sarah Dixon, who has worked with foreign royals and friends of the royal couple's. "If a baby is used to the nanny and you pass them to Mom, they can get a little fidgety and anxious - but he was so happy with both Will and Kate."

As they have since the early days of their romance, the couple remain committed to fostering close family ties with the Middleton family. "Royal in-laws have never been as conspicuous as the Middletons are," says royal biographer Christopher Warwick. Including Carole, Michael, sister Pippa and brother James in the christening photo "was definitely a statement by Kate and William that the whole family will raise this child," says British maternity wear designer Rosie Pope, "and the whole family will be a part of them ultimately being King and Queen one day."

As George goes from snoozing to smiling to soon-to-be sitting - "He's gotten so big recently," William told a well-wisher last month - his family are head-over-heels in love. "Carole and Mike just love him absolutely more than the world and are spoiling him rotten," says Fidler, who joined the Middletons for a drink at a pub in their hometown of Bucklebury a few weeks ago. "Mike has got a huge beaming smile on him at all times. They are just overwhelmed to be grandparents." Even the normally reserved Prince Charles gushed about George in a rare interview with TIME. The little prince, he said, "is what this is all about." A family friend who recently met mother and baby says Kate was "very relaxed" and "glowing." The little heir, meanwhile, "was wrapped in a blanket, just taking it all in. He is just like any little baby, and she is a happy mum." And the happy milestones have only just begun.