mrwinchester, it sounds terrible, but my spouse and I choose the birds to get "processed" first by choosing the noisiest, most obnoxious ones that pick on their brothers or sisters. I'm the only one who processes them (like you, I have a soft-hearted spouse), but it makes it easier.
One Cornish Cross was given grain to supplement forage, and made it to nearly six months old before he met his end. The people who ate him exclaimed that they thought he was a turkey, because he was so huge.
For nice, tender babies, you could get a baby scale and check their growth that way? Or just eyeball them, and harvest them a few at a time as you want game hens for dinner?