The viewpoints on another thread are so far from what I considered "an obvious truth" I have to ask.
Would you leave a young child, a two year old, with an agency nanny you and they have never met before? For a social occasion, not a medical emergency?
Think no other childcare, rather than life or death situation.
Personally I would only leave my child with a very small number of people - one grandparent alone. Other Grandparents as long as an aunt/uncle of the child also there (grandparents are old). Mine and DH siblings - 2 or 3 out of all of them.
Friends - in a medical emergency, not for a night out.
YABU - I would definitely leave my child with an agency sitter they didn't know
Yanbu - I wouldn't leave my child with an unknown sitter, I'd skip the night out