Using 4 lights for the high key setup, the front pair were 150W (one soft box, one umbrella) , with 2 x 400W sofboxes for lighting the background. As high key entails having the background around 1-2 stops brighter than front, it is usually advisable to place the more powerful lights at the back.
This proved to be correct in this shoot, as front lights were on 90% power vs 40% for backs.
When photographing the subjects sat on the floor, or even lying down, you have to lower the height of the studio lights accordingly, to ensure a nice balance.
For the window light shot of Chris & daughter, they sat approx 1 foot from a large window, whilst a golden reflector was held to the right of their faces, to bounce some light back in to the shadow sections.
Matt’s window light shot was taken approx 12 feet from the window, with no reflector. Using f/1.4 gave a very short depth of field to the shot.