The girls left, and returned holding a glass bottle containing red liquid. The bottle was large compared to their height. One held it, in two hands, cradling it protectively, and vigilantly attending to its safety. The other stayed close, watching too, in case the first failed in her duty.
They were instructed to put the bottle back, because they already had one at home. As they left, the second mother said, "Don't drop it." Hearing this, the first mother was spurred to action and said, "Be careful, it's glass." Satisfied, the parents resumed talking without a further glance to their daughters.
As the girls walked away, the bottle carrier replied, "I know."
In general, it is unreasonable to give advice to someone when you know less about the situation than he does, and have no reason to think the advice will be useful. We can infer that the children had heard this advice many times previously. This is noticeable in the casual way the mothers said it, the overly-careful behavior of the girls, and the "I know" reply.
A good parent would think about what his child wants, and use questions and observations to help him understand, and then find ways to be helpful. These parents gave advice tailored to any child of that age and never, in all the times they've repeated it, watched to see if the children were careful or not. They simply assumed their children did not listen to them, or that all young children are careless. And they gave the advice anyway, with no reasonable expectation that it would help anyone.