Family A has a nanny but she can't drive just now.
Family B mum down the road says she's happy to pick up Family A's kids on Tuesdays.
Family B mum starts to pick up regularly. Nanny sends regular text on Tuesdsays "ok to pick up?" etc.
Family B takes their holiday abroad one week so family B mum doesn't respond to text - is at a wedding abroad. Family B has made vague reference to wedding to mum of Family A over coffee previous week but not in a "so you realise I won't be picking up Tuesday don't you?" kind of way.
No-one picks up kids, school call Family A dad who is very cross with Family B and sends nanny down to school in a taxi.
Jury, verdict please....