Is a sibling with chicken pox dangerous to my 7 month old baby?

Not particularly: The 7 mo has likely been exposed enough to become infected, with the 1st day of exposure likely the day before the spots appeared. Incubation is 10-21 days. It is seldom a terrible disease in infants. They usually have fewer spots or complications but it deserves monitoring. Discuss the situation with your doc.

Depends: They may have both been exposed to the same source at the same time & break out differently within the usual range of 10-21 days from exposure. If not, the 2nd began exposure from a day before the spots appear.Simply being in a room together with a case for 1/2 hour is enough to pass it. Infants seldom have as many spots or complications as average kids. It is worth monitoring & a call to your doc