going out without baby?

Basically my birthday is in April and my son will be 9 months, it will be the first time I've ever gone for a night out but some people in my family are saying I'm selfish because apparently I shouldn't ask my mum to babysit for me (even though she has already said she would) and I should be home with him all the time, I have never even gone out with a friend without him, do I not deserve one night?