Part of the increased consumption and higher costs associated with children over adults is that the child, and the situations one is trying to correct/treat, are always changing.
It's not as simple as sending off for a new pair of glasses because OOOPS! you sat on the last pair. The prescription changes as the child grows, as his head grows and his eyes grow. So you can't simply replace the glasses. It's off to the optometrist or, depending on the shape of the child's eye and the rate at which his eyes are changing, perhaps an opthamologist.
And it's not the cost of the individual pair of shoes. It's the cost of the shoes x 2 EVERY FIVE MINUTES.
Of course not one of these things will derail an ERE plan, nor will any one of these things consume $12k/year. But these ongoing monthly costs can easily mean that the kids consume the vast majority of a monthly budget.
I'm betting that if your mom would have a slightly different recollection of the routine childhood illnesses than you and your sister.

We haven't even talked about chicken pox and pink eye and all of the other stuff.

My kids weren't particularly sick. Ear/throat construction (two rounds of ear tubes with some other surgical alterations) contributed to a lot of the upper respiratory stuff.
Asthma runs in my family and one of my kids was unlucky enough inherit a pediatric/exertional version of it, along with my seasonal allergies. That complicates upper respiratory stuff as well.
Otherwise the boys were exceptionally active and athletic.
The point is that we are quite typical- these are not exceptional situations nor exceptional costs.