100% with Suzie_Homemaker; I've seen even caregivers waiting for the siblings to come and families have changed their mind almost when hey had to start (a nanny was more convenient) so, the poor caregiver was.left on the air.

In my group everyone knows that I'm not flexible. I do my best to post my openings way ahead (usually school age children leaving) and it is up to them to take the spots or not. Also I post the rate and non negotiations from there (ex. Sibling discounts), my materials, my time and dedication, the food and all other expenses do not give me a sibling break or discount.

I do not know when they came up with the "siblings discount" term. All the services and time consumption still same. So for me my rate is a non negotiable factor.