Be sure to read the comments.
I scanned the article and read the comments. One comment pointed out what I had already thought about: it could take a lot more virus to make a young kid show symptoms, and very few children would manage to get there. But the few that did would have higher virus loads, but that does not show that these rare children are efficient spreaders, and even if they are, they may be so rare that they can’t have much effect. Also pointed out was that all the children in the study were already in the hospital and it was a very small number studied.