Even some of the first-team players had to tread carefully around them - not to mention the hapless purple-clad chiropodist whom they locked in a room for three hours just for laughs - but, for one of them, there soon came a point when the horseplay had to stop.
It was November 1998 when Steven Gerrard finally got the call to make the step up to start training with Liverpool's first-team squad. Stephen Wright, the aforementioned Wrighty, was summoned to Melwood on the same day, but it was Gerrard who had really caught the eye of Gérard Houllier, the club's new manager. Houllier took him to one side. "This is where it starts," the Frenchman said in the paternal tone that would become familiar to Gerrard over the next five-and-a-half years. "Do what we tell you. Eat what we tell you. Drink what we tell you. We want you ready for the first team. You're not far away."
That was the day it all changed for Gerrard. He had always been focused on his goal of becoming a professional footballer for Liverpool - and, contrary to what Houllier has occasionally claimed, was always expected to make the grade, having been identified as a future star from an early age - but focus turned to obsession.
Like a carefree sixth-former who is told that he should be setting his sights on Oxbridge, he knuckled down and raised his game in every respect. He changed his diet (no more burgers), he changed his attitude (no more larking about or answering back) and he treated every training session like a cup final. By the end of his first week at Melwood, he was running rings around Paul Ince, the club captain and a mainstay of the England midfield.
The breakthrough came on November 29, 1998, ten years tomorrow, as he was sent on as an 89th-minute substitute for Vegard Heggem, at right back, in a 2-1 victory at home to Blackburn Rovers. It was one of those substitutions that is designed to eat up time - and, among the majority of the 41,573 crowd at Anfield that day, there was little sense that a star had been born in front of their eyes - but, having got a taste for the big time, Gerrard did not want to give it up.
He started at right wing back the next weekend against Tottenham Hotspur, marking David Ginola. He felt afterwards that Ginola, who would be crowned Footballer of the Year that season, had humiliated him. To Houllier and everyone else, the 18-year-old had come through what would be one of the most searching examinations of his early career.
Gerrard was a little raw in those days. He was also gangly, the result of a sudden growth spurt, and felt that his first responsibility to tackle rather than drive his team forward in the dynamic manner that would become his trademark. As a consequence, he looked at times like a boy trying to make an impact among men, throwing himself into tackles that would leave experienced pros wondering who was this skinny kid with the bowl haircut. In a match against Middlesbrough at Anfield, there was a running battle with Paul Gascoigne, whose videotape, Gascoigne's Glory, he had all but worn out in his early teens.
As they left the pitch at the end of the game, Gascoigne, by now in decline, told Gerrard: "You are a f***ing good player. Keep it up." Gerrard has kept it up, all right. Over the past ten years he has emerged as one of the most formidable players in world football. Primarily a destructive midfield player and an infrequent goalscorer in his early days, he has been converted by Rafael Benítez, Houllier's successor, into the fulcrum of Liverpool's attacking play, a player with the energy to drive the team forward and the creative flair to break down defences, often finishing things off himself with that sledgehammer of a right foot.
In his first five-and-a-half seasons, spanning the Houllier era, Gerrard scored 28 goals. In the past four-and-a-half years, under Benítez, he has scored 76. That is not necessarily to say that Benítez has made him a better player, merely a different one. Gerrard would have been world class at whatever he was asked to be, even at right back had that been his fate.
And yet, for all the heights that he has scaled, there is a feeling within English football that he has even more to offer. Certainly that applies to the national team, where he has never really come close to replicating the influence that he exerts as a matter of course at Liverpool. Even though he has played in just as many different positions for his club, he feels that his role for England has been far less clearly defined, as he is asked to fill in around others rather than take centre stage.
His struggles in an England shirt are a rare source of frustration in a career that has taken him to heights that few players can even contemplate. The incredible, unforgettable Champions League final triumph over AC Milan in Istanbul in 2005 is the most obvious, along with a similar rollercoaster ride in the FA Cup Final against West Ham United 12 months later, but they are far from isolated highlights, even if the Premier League title has so far eluded him.
Popular theory would suggest that, at 28, Gerrard should now be at or approaching his peak of performance. There are no such guarantees in modern football, with the experiences of Ronaldo and Ronaldinho, not to mention Michael Owen, suggesting that peaks may come in the early or mid-20s, but Gerrard defies that unwelcome trend, just as at times, in a Liverpool shirt, he has appeared almost to defy reality. Not bad for a self-styled scally from Huyton.
Little wonder that Boggo, Greggo and Cass, having seen their aspirations fall by the wayside, now live their dreams through him, much like Liverpool fans from Bootle to Bangkok.