Now, after reading the whole thread...
I think they look like a Blue Silkie X Birchen Cochin. Is this a possibility, Candace? I am assuming these are from your flock?
They are GORGEOUS with or without rumps. But another option to consider, if you are line breeding at all, I had a woman across town tell me that weird things like that happen when the lines cross too much. Something to consider. I trust her since she has been raising chickens for a long time. She actually came and bought one of my extra Jaerhon cockerels because she was starting to get some rumpless birds out of her Jaerhon flock that she needed new blood after 5 years.
And Candace, the 3 SLWs I had hatch from you are a trio! How fortunate can I be??? They are doing great and I love them. Can't wait until they lighten up, but they are starting to. I will send pics once I have them running around outside. The kids in my daughter's second grade class loved holding them the other day. I think it mellowed the chicks down a bit.