Is this one of the best things or one of the worst things you can say to your children?

It's relative.  Saying it to my children would be wishing them sweet girls.  My grandkids.............different story.

                "The Mother's Curse"

Neither. Who are you? Both as a parent and as a person? Good, bad, a little of both? Is it really the best wish you can have for your kids to be copycats of you, rather than their genuine, individualistic selves? These are all important questions to ask in this context.

Also, just consider these quotes by Kahlil Gibran: 

"Your children are not your children.
They are the sons and daughters of Life's longing for itself.
They come through you but not from you,
And though they are with you yet they belong not to you."

"You may give them your love but not your thoughts, 
For they have their own thoughts.
You may house their bodies but not their souls,
For their souls dwell in the house of tomorrow, 
which you cannot visit, not even in your dreams.
You may strive to be like them, 
but seek not to make them like you.
For life goes not backward nor tarries with yesterday."

I'm just glad I have a boy, he is just like me. Creepy. A hellion boy I can take, a girl... with the knowledge I have as a female??? That's an earlier grave just waiting to be filled. No thank you!

Since it happened to me a few days ago from my dad and his 23 year old girl friend, "You're going to be a brother" fudge! I'm 31 and have kids of my own I don't want to know my dad did anything with his girlfriend. Eek!