When you say you thought you were done with kids, was that both of you…more you than her?
As mardybum says, there is only one way to be sure, otherwise there’s always going to be a chance of another one appearing.
However , it is what it is now and once ‘it’ comes along, you’ll no doubt fall in love with him/her and off you go again. You never really are in control of your life anyway, always something sidelines it, so it may as well be a good news sideline like this, rather than some of the bad news options.
Congratulations BTW.