Letting the 6 year old go makes the most sense. However, I wouldn't jump the gun and tell the family until you know 100% sure that the new baby will be attending. Probably a month in advance would be plenty of time for them to find another caregiver. The reason I say this is that we all know how unpredictable families can be and as much as we want to take people's word. Things always change and you don't want to be hooped. Good luck