Here's a virtual image of the 'setup' before the kid fell (as compiled by ABC news after witness statements, etc...)
Now I know this isn't exactly smart, and it's not what most of us would probably do. At the same time - that happens at zoos. That's something you'd often see a parent do, especially if the kid can't see the dogs underneath. Now I think my parents (or me personally, had I any children) would probably just try to lift the kid up and hold him there, but this is a woman and isn't going to have the upper body strength.
So what did she do? Well, the nearest substitute - hoisted him up and set him down. She probably had her hands there ready to catch him if he bobbled...and didn't get it done. Our parents likely did extremely similar things at points during our infant/toddler years.
As you start to look at this a little more and listen to interviews from neighbors, etc...; this really does appear to be a pretty doting parent that just made a very poor judgment call, but not a judgment call that we haven't seen before in public settings. And I can't imagine she knew that these were essentially the most savage damn things in the world, so it didn't even occur to her to be hyper-cautious here. If those were lions, I'm betting you don't see her try to do this because you have your radar up.
I think I'm just going to chalk this up as a pretty damn horrific accident. But for the grace of God go many of you.