I have made children using the following method:
1) Scale the full body of the character down to the lowest you can.
2) Use the "Bake" key, which is located on the top and right part of CC (it has a toast icon). This resets all morph sliders to 0, while keeping intact all the morphs you have applied. So now you have a scaled down character, and the option to scale him down again even more because the slider is reset. Scale it down and bake again if you need a really small kid.
Maybe the webinar says that exactly, I didn't have time to watch it.
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