Do your kids with SAD symptoms get only depressed in winter months (or other seasons) and "normal" the rest of the year? Or are they also manic, or happy or high, at other times? Do you keep a mood chart? There is a great one for Bi-Polar, you can find online, but this might also be useful for you or your kids who have other types of mood swings. Charting can really help you see the big picture, and over time it helps you realize what the triggers are. It won't solve the problem. But sometimes just knowing, OK, I am on a downward swing now because of X Y and Z, can help you cope. I'm a very moody person, not SAD but bi-polar, though much more on the happy side than sad side, which is why it took 44 years to find a diagnosis. But my son takes after me, and is very moody, so I keep a watch on his moods.
He is very moody, even in summer, he's just much easier about it. There is a history of depression on both sides of the family, though not bipolar depression (I have to admit, on bad days I have wondered). I'll check out the mood charts.