It's not a case of judging, it's a case that we have a responsibility to not put a cat somewhere it will almost certainly be run over as you really can't stop a cat from wandering onto a road. As it happens, Millie is miles and miles away from you so probably wouldn't have been suitable for you anyway but you do have to think about the danger that traffic poses to a cat. Especially a young cat of only 6 months old who has no street awareness. Main roads and outdoor cats just don't mix. It would be absolutely tragic for you and the cat if it were to be killed on the road, not to mention the heartbreak it would cause to your child who had recently bonded with the cat.
Have you considered a cat who needs to be indoor only, eg. a cat with FIV? That would be the kindest option as it means you can provide a lovely home and the cat would be safe.