I have a 3 month old DS. I recently saw a friend with her toddler DD. A couple of days later she called to say that her DD had been exposed to chickenpox the day before she saw us - the other toddler's rash had just come out.
As far as I can tell the incubation period is 2 weeks and you're only infectious at the end of that - so even if her DD is incubating chickenpox she won't have been infectious when we saw them.
AIBU not to quarantine my DS?