Please don't feel bad!

I'm sure that you in no way neglected your child.

It's impossible to know absolutely everything about someone's condition. Besides, there are now routine imaging and diagnostic tools that weren't available 50 years ago.

I'm an example. All my life, people made fun of the way I walk. It was dismissed as laziness on my part.
When I was 39, I had a knee Xray and learned I have a birth defect in my legs; my lower leg bones are fused. With no flexion in my lower legs, my walk was both stiff and bouncy, plus it put a lot of strain on my knees and ankles. (And since having a stroke, I can barely walk at all.)

It never occurred to anyone that I had a skeletal problem. Just the way things are.

Don't be hard on yourself.