previous post explored the generous definition of childhood that underlies the claim.
In 1941, according to Statistics Canada historical statistics, the population of Canada was 11.51 million.
The same source shows that between 1861 and 1941, the period during which the vast majority of home child immigration occurred, there were 5.84 million immigrants to Canada. The ratio of the two figures above, 11.51/5.84, is 1.97.
Applying that same ratio to the number of home child immigrants, taken as 120,000, gives an estimate of the population of home child descendants of 236,000. That's about 2% of the population in 1941. Taking a more frequently quoted figure of 100,000 child immigrants they and their descendants would account for an estimated 1.7% of the population in 1941.
Since that time the number of people coming to Canada has ballooned while the natural increase due to births in Canada has declined. One would expect the present day percent to be substantially less.