Because the child I'm worrying about is my third!
The teenage daughter of a friend is babysitting for me tomorrow night for the first time. I've never had a teenage babysitter before.
I'm not worried about ds1 and dd, they'll be fine. But 3yo ds2 has never been put to bed by anybody other than dh or me, very occasionally by my mum. Will he cooperate? Will she cope if he doesn't? Will he miss me and get upset? Will she cope if he does?
Oh worry worry worry.