Stab3.5up,
You are quite right, you could indeed add cyber children, I cannot see them refusing you to board if the children didn't show. There is zero tax so this is a cracking offer.
Kids Fly Free with British Airways this Summer
This is a good source of info on such matter and a great way to ramp up your mileage, this might get taken down if it is perceived as promoting the site. Though it is a good source of information, more than selling something per se.
EI-BUD