Walking pneumonia. This term simply means that the infected patient need not be hospitalized or remain in bed. It does not indicate the causative agent, which is essential to know in order to assess the risk of transmission to others. If this turns out to be mycoplasma the answer is that in 4-6 weeks any other member of the family may become ill. If your 8 mo old develops any symptoms have them seen asap.
Walking Pneumonia. Yes. I know this is an impossible task, but do your best to keep them apart. Additionally, make sure you and everyone else in the house are washing their hands when going from child to child.
Infectious . If your 8 year old has an infectious disease such as a pneumonia caused by a virus or bacteria, then there is a possibility that other members of the family may have the same illness. It does not necessarily mean though that the baby will have pneumonia. It may present as an uncomplicated cold or ear infection.