Myhill returns to the squad with regional experience after appearing 11 times for the Scarlets since August 2011.
The squad are without last year's Liam Williams who made the step up to the senior team in Gatland's autumn squad and retains his place in the RBS 6 Nations training squad.
The U20 team will play all their home matches for the first time in North Wales at Eirias but first head to Dubarry Park to face Ireland on February 3.
They return to Wales to play Scotland on February 10 in the first of three home matches at the new North Wales facilities.
Head Coach Danny Wilson is confident in the new blood and believes those involved last year will bring some knowledge and experience to the squad. "It's an exciting young squad we have here, this group of players have trained well over the past few weeks, there's a fair amount of talent in the wider squad," he said.
"We're looking forward to a tough challenge against Ireland away and preparations are going well.
"We're all excited about the change of venue to Eirias in Colwyn Bay. The facilities are superb, we're hoping to get a good crowd in from north Wales and promote the U20's in this area.
"We will be settling in and making Eirias our home ground and I know rugby is well supported in north Wales and we would love a good crowd to come along and support the U20's and make Eirias a difficult place for opposition to visit."
2012 Wales U20 Six Nations Squad:
Rob Evans. Club: Llanelli, Region: Scarlets
Tom Davies. Club: Cardiff, Region: Blues
Dan Suter. Club: Bridgend, Region: Ospreys
WillGriff John. Club: Cardiff, Region: Blues
Kirby Myhill. Club: Llanelli, Region: Scarlets
Jamie Sollis. Club: Cross Keys, Region: Dragons
Matthew Screech. Club: Cardiff, Region: Blues
Jack Jones, Club: Swansea, Region: Ospreys
Rhodri Hughes. Club: Swansea, Region: Ospreys
Ellis Jenkins. Club: Cardiff, Region: Blues
Daniel Thomas. Club: Llanelli, Region: Scarlets
Dan Crimmins. Club: Cardiff
Rueben Tucker, Club: Cardiff, Region: Blues
Jonathan Evans. Club: Bedwas, Region: Dragons
Joshua Davies. Club: Newport, Region: Dragons
Jack Moates. Club: London Irish
Jordan Williams, Club: Llanelli, Region: Scarlets
Sam Davies. Club: Swansea, Region: Ospreys
Lewis Williams. Club: Pontypridd, Region: Blues
Cory Allen. Club: Cardiff, Region: Blues
Nathan Edwards. Club: Bridgend
Luke Williams. Club: Cross Keys, Region: Dragons
Luke Morgan. Club: Bridgend, Region: Ospreys
Iolo Evans. Club: Llanelli, Region: Scarlets
Jake Randall. Club: Llandovery, Region: Scarlets
Ross Jones. Club: Bridgend, Region: Ospreys
Ireland v Wales, Dubarry Park, KO 19.05- 03/02/2012
Wales v Scotland, Eirias, KO 19.35- 10/02/2012
England v Wales, Twickenham Stoop, KO 19.30- 24/02/2012
Wales v Italy, Eirias, KO 19.10- 09/03/2012
Wales v France, Eirias, KO 19.35- 16/03/2012