I guess that whatever they find in terms of links, there are always exceptions...

I skipped crawling altogether and mum had to deal with me walking around at 9 months...

No learning difficulties here, highly academic the whole way through. Could read before I started kindy, always aced the spelling tests through primary school, maintained the top class through high school with no effort and was dux of my school with minimal effort in the senior years.

Hopefully there are enough stories here that will reassure you that there's no hard and fast rule that states your child WILL have problems if they skip crawling.

BW