I think you misunderstand. There is obviously another caregiver looking after them. I can't have a 24 hour open door policy with my kids while I'm working from home, just the same as anyone who works in an office.
Then it is perfectly reasonable to have a closed door for calls. However, even in that case, I would not mind an interruption or two during the call. Any more though, I'd start questioning the role of the caregiver.