Hmmm, I would honestly have a hard time deciding which to choose if I were in your position also.
I can see your concern r/t NICU and spending time w/ your children. That could be rough. But w/ the NICU, I wouldn't worry that if you start there, you'll have problems transferring to a different floor someday. If the unit you decide to want to transfer to one day hires new grads, they'll hire YOU no matter where you started your nursing career.
I don't have much nursing experience myself (about 4 months), but I know when I worked in ortho as a PCT, it was a very demanding job. It was just as demanding for the nurses too. Just as a comical sidenote... I've heard a couple of em say they just feel like drug pushers w/ all the pain meds they give out!
And don't worry soley about developing the skills. In OR, I'm sure you would learn TONS of info r/t pathophysiologies w/ interventions of all sorts of things! This, you would definitely be able to take w/ you to whatever area you'd decide to go to next. Skills are important to learn, but are fairly easy to learn compared to the other things we must learn in nursing.
I think what it comes down to is you deciding what is of higher priority for NOW. Spending the time w/ your children? Working where you LOVE? Being where you're comfortable and have lots of support/help? The days and hours? Wanting to challenge yourself?
And I emphasize NOW b/c you can always change things. You should not feel that if you decide to work NICU, you are placing that as a higher priority than your children. (I realize I might have made it sound that way, but I didn't mean for it to.) Of course, your children are of high priority. Like one post said, you'd still be able spend 2 days/week w/ them. You just need to decide if that will work for you for THE TIME BEING.
Wherever you go, you'll gain knowledge and experience. And that is what counts. Good luck in making your decision and best wishes!