I only exclude the child with the actual symptoms.
It would be kind of silly to exclude the sibling too.
Lots of kids can be carriers of an illness/virus and not actually get sick.
If we exclude because of the possibility of the other child being contagious too, then schools would do it as well.
My own children RARELY caught the same illnesses.
My DD got strep all the time, my DS has never had it.
Here are some other threads about sibling illness and exclusions
https://www.daycare.com/forum/tags.p...ibling+illness