I am not familiar with any sources like you mentioned; however, I am not sure the extent to which you could consider members of the 12th S.S. to be child soldiers.

The 12th S.S. Panzer Division was a frequent adversary of the 3rd Canadian Division, which shouldered the burden of Canada's early fighting in the Normandy campaign. While many of its officers and N.C.O.'s had battle experience, the remainder of the division was indeed exceptionally young and "fresh from the military fitness camps of the Hitler Youth". However, between the time at which the division was raised in May 1943 and the time it entered combat in June 1944, many of its recruits had passed their eighteenth birthdays. Indeed, there were discussions within the German military as to whether these young men were entitled to normal "adult" rations of things like cigarettes once many of them started to turn 18. Prior to that, in lieu of cigarettes or alcohol, members of the 12th S.S. received rations of sweets during their training.

By the time the division first saw combat in June 1944, the majority of men were likely past their 18th birthdays. A look at one battalion for instance (1st Battalion of the 25th S.S. Panzer Grenadier Regt.) in that month shows that 65% of its total strength was made of 18 year-olds. While one battalion can only provide a cross-section of the division, it is worth noting that the majority of the men were 18 or over. If these numbers held across the rest of the division, then most of those who the Canadians fought against would have been young adults. With that being said, the relatively young age of the 12th S.S. did have telling effects on the battlefield. Historian C.P. Stacey stated that

The division was to show in action the characteristics which its composition might lead one to expect: reckless courage and determination combined with a degree of barbarity found perhaps in no other formation.

It was therefore the almost suicidal bravery of these young men -- a result of the ideology-soaked training regimen of the S.S. divisions as well as their youthfulness -- which primarily stuck out for the Canadians. Stephen Hart relates how one of the regimental commanders within the 12th S.S., the infamous Kurt Meyer, instructed his men that they were authorized to execute any officers or N.C.O.'s who failed to show offensive determination. Since the German army in Normandy was primarily in retreat, this culture within the division tended to manifest itself in the exceptionally dogged defences it mounted against the Canadian advance. For instance, when Canadian forces entered Falaise on 18 August 1944 they encountered 60 members of the 12th S.S. who were surrounded in a school. After a 48-hour siege, the Canadians only captured six of S.S. alive.

There was also a variety of war crimes committed by the 12th S.S., including on the first day it saw combat on 20 June 1944, when Meyer ordered the execution of some 20 Canadian prisoners of war at the abbey in Ardenne. Hart estimates that the 12th S.S. executed 93 Canadian POWs between June 7th and 12th in 13 separate incidents, most of which were sanctioned by officers of the division. This was probably another factor which coloured the perception of Canadian troops that these were not children they were dealing with, but rather dangerously fanatical young men.

I'm sorry that doesn't precisely answer your question, but I hope it helps!

Sources:

C.P. Stacey, Official History of the Canadian Army in the Second World War, Volume III: The Victory Campaign

Stephen Hart, "Indoctrinated Nazi Teenaged Warriors: The fanaticism of the 12th SS Panzer Division Jitlerjugend in Normandy", in Fanaticism and Conflict in the Modern Age