With the trycyclic antipressants, just about all the studies showed weight gain. With the SSRI's, some of the studies go one way (as in your links), others go the other, and some show no differences. Also, a lot of these poor kids are probable taking Ritilin, Adderal, Buspar and/or Wellbutrin on top of their SSRI, radically changing the picture.
One thing to keep in mind is that weight loss is a depression symptom. Some of the kids getting the SSRI are too thin, so weight gain can be a good thing. To be meaningful, studies have to take into account the whole clinical picture including what the person's weight trend way before starting to take the drug.
Looking at the bottom half of this link one can see some of this:
Again, I'm not saying that it's good for lots of kids to be on all these drugs. Also, I'm not saying that the article by Drs. Sussman and Ginsburg is bad. I think they did a nice job even though their article is not the last word by any means. I also think that the good doctors would agree with me that the older tricyclic antidepressants were more associated with obesity. So even if Sussan and Ginsburg are right, which is far from proven, this would not in the least explain the epidemic of childhood obesity.