It wasn't adjusted to exclude traditional non-working categories of any kind at all. That's what made is such an obviously useless figure, right there in the first sentence.
Sure, but some of those non-working categories (in particular, students and retirees) could arguably go into the workforce if sufficiently motivated, and might be assumed to be a small portion of the population. Children seems more unequivocal - and thus deserving of calling out specially (while remembering that this is in addition to those other categories).