In this case my mum. I have a beautiful 5 week old boy and have been invited to a night out when he will be 8 weeks old, his dad is working that night so I would require my mum to babysit for the first time.
My mum has brought up 2 kids and she is the only person (other than his dad) that I would trust (for a very long time!) to look after him. Both his dad and my mum are happy for me to go out that night and for her to look after him but 8 weeks is so young! Plus I won't just be able to pop home if something happened as I'd be an hour away and it would prob be for 6 hours or so.
How old were your children when you first left them? Am I being selfish even considering this? I feel a bit guilty already at the thought! I'm totally undecided at the moment.