MD, are we always looking at the same sort of stuff?? I have just been looking into this in the past week or so and read the same thing.
LOL! Apparently so.

My reading didn't stray into the realm of infants, but I did notice a kind of negative feedback loop where sleep deprivation = brain damage (probably incremental) and brain damage = disturbances to sleep patterns. Which kind of leaves people like me with incurably broken sleep up Foofer River (well, for now, until they crack the solution on how to scrub those bad chemicals out of your brain). That's one way to look at it. On the other hand, armed with this knowledge, we also know that any improvements we can glean in either quality or duration of sleep can have a positive, curative effect. And there are many different ways to get improvement to sleep. That's why I'm all about the colour of lighting, and turning the telly off, and wakeup times, and the magnesium/Vit D/calcium supplements, and even just taking the family along on an attitude adjustment ride (yes, I've borrowed every junior reader from the library that deals with the topic of sleep, for Miss E's benefit). I'm personally resigned to the fact that I may never stop feeling tired, BUT I'm damn well going for an improvement in brain function, any way I can.

For Miss A, I'm sure you will ask lots of probing questions. If her sleep is still poor, it might be a good idea to get her screened for apnoea/other sleep disorders. But be prepared for the answers on that front to come back as a vague "nothing identified". I understand that kids with conditions like ADHD can often have very poor sleep (and I'm sure you've already read/considered that) but it's unclear which direction the causality flows. A lot of that will be outside your control, but some of it you may be able to influence using things like strategic sunlight exposure, as well as nutritional supplements, attention to food chemicals, etc.