That whole "all girl babies" thing is just BS ol' wives tale. My first (a son) was born while I was in serving on a sub. I was there for the birth, but not the first few months of his life. My second two were after I was out (by a decade for the 2nd and 14 years for the 3rd) and both are girls.
Putting something on your dreamsheet is a crapshoot. I went to prototype in Idaho. I requested Charleston, Groton, and San Diego... I got Bangor. Feh... worked for me.
Having kids while you are in is TOUGH. In the pipeline makes a hard thing even harder. Wait until you are to your first command. You'll have more money, a bit better conditions, and more importantly SHE will have a better support network in the other wives on the boat. Keep in mind you WILL be gone at least half the year regardless of class of boat you get, maybe more, but not less (provided you're not in the yards in which case it's the cursed "in port" but you'll WISH you were underway). Regardless your wife will HAVE to get to be self sufficient. If she isn't now, GET HER THERE. If she needs you to take here everywhere, break her of that habit NOW. You are freaking casper once you are on the boat. You might be there, but you really aren't there. She's going to have to deal with the dog puking, the car busted, the dishwasher spewing dishes across the house, etc all with out you. Make sure she can do that now.
PreComm isn't bad if you get there at the endish, sea trials are a bit of a beeotch, but stuff like DASO is kinda fun. Certainly not the first crew up though.