If you want to see what a Cochin should look like, see my Avatar. He is a standard sized Black, but that is generally what they should look in shape and appearance.
This is what a white bantam should look like.
https://www.cacklehatchery.com/white-cochin-bantam.html
Your parent birds could be culls from someone's personal "Silkied Cochin" project so they have the recessive silkie feathering in their genes, but they don't exhibit it.