Having one of those knights where I feel like a failure of a parent.

I think all you can do is love them, let them know they are loved and do your best. Often, in retrospect, we think of how we could done things better, well, save that for the next time and don't beat yourself up for not seeing it at the time. The other thing is be mindful of what you say. Words are extremely powerful for good or bad and once said they can never be taken back. Best wishes.