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From the first link: Update: "... it's really quite straightforward. I'm not sure if telling you exactly makes it less magical, but yes, Photoshop is involved."
I'm guessing she sets up the camera on a tripod, photographs the scene with nobody in it, goes back into the scene with Henry and takes a photo while giving him a little bounce, and then sews the two images together so she's no longer below him.
Specklet beat me to it. Those are antigrav infants. Probably engineered in Area 51, or maybe just gifted. Mixed human/angel parentage or such. Happens all the time.