Ulster's top tryscorer Craig Gilroy and Leinster flier Andrew Conway are included along with Dominic Gallagher and Kieran Marmion, who were not involved at all in the Six Nations campaign.
Ruddock's men could not face a tougher start to the tournament with Grand Slam winners England first up followed by an encounter with South Africa, who finished third last year, just four days later.
The former Wales coach admits they will need to raise their levels of physicality as the games come thick and fast in Italy.
"Absolutely we need to win one of those matches [England and South Africa]," Ruddock told the Irish Times.
"I haven't finalised the team against England yet but it's floating around in my head.
"You are talking about eight or nine changes to the team that lost to England in the Six Nations.
"In the Six Nations we changed week to week because of different demands on players. We have more cohesion for this tournament.
"In many ways it's the Olympic Games of rugby for these lads as it only comes around so often. It will be savage.
"Certainly the physicality that England are going to offer and then the turnaround in just a matter of days.
"As I said there were too many lads dropping off tackles last time, going to high. We've got to go low, we've got to chop them, put them on the floor and then put some heat on the ball there after. That's the big message. It can be done."
Ireland Under-20 squad for the IRB Junior World Championships:
Niall Annett (Belfast Harlequins - Ulster)
Finlay Bealham (Belfast Harlequins - Ulster)
Andrew Boyle (UCD - Leinster)
Shane Buckley (Garryowen - Munster)
Conor Carey (Ballymena - Ulster)
Aaron Connely (Galway Corinthians - Connacht)
Andrew Conway (Blackrock College - Leinster)
David Doyle (UCD - Leinster)
Peter Du Toit (UCD - Leinster)
Tadhg Furlong (Clontarf - Leinster)
Dominic Gallagher (Dublin University -Ulster)
Craig Gilroy (Dungannon - Ulster)
JJ Hanrahan (UL Bohemian - Munster)
Iain Henderson (Queens - Ulster)
Paddy Jackson (Dungannon - Ulster)
Michael Kearney (Clontarf - Leinster)
Alex Kelly (UCD - Leinster)
Brendan Macken (Blackrock - Leinster)
Kieran Marmion (UWIC - Exile)
Luke Marshall (Ballymena - Ulster)
Eoin McKeon (Galwegians - Connacht)
James McKinney (Queens - Ulster)
Jordi Murphy (Lansdowne - Leinster)
Tiernan O'Halloran (Galwegians - Connacht)
Daniel Qualter (Buccaneers - Connacht)
James Tracy (UCD - Leinster)