So having a kid definitely opens the door to a LOT of potential quality material, but I haven't quite gotten the hang of taking some candid shots. My daughter attended a party for a toddler where there were TWO mothers-to-be. One was okay, but the other was STUNNING. I also had to stop by a kid/baby store to pick up a gift. There were SEVERAL good-looking expectant ladies, and one BEAUTIFUL redhead among them. Tried as I might, I wasn't able to get ANY good photos. Not a single one! I thought perhaps those more experienced than I could chime in with their secrets. It would benefit the community.

I will add that I found a SWEET app on iTunes called "Fast Camera." It basically takes rapid-fire photographs. I think it does this by recording video and just removing still shots from the video file. However it works, it seems to do a pretty decent job. It also has a "stealth" mode with blacks out the screen so onlookers are none-the-wiser. It does advise the user to turn the sound of to prevent the camera sound from giving anything away. Hope this helps!

#1 tip for getting good candids. Don't take photos. Take videos. Videos are much better and you can always make photos out of videos later if you want to. I've never taken a photo in the couple or so years since I started doing this regularly. A photo is just a photo, but there's nothing like watching a beautiful pregnant woman acting naturally in a video.
I use an iphone app called Quick Spy Camera. It records HD 1080p videos as long as your iphone supports it, and blacks out the screen making it look like your phone is off.
So if you're standing near a preggo, let's say 10 feet away, just pull out your phone, launch the app, and stand there minding your own business, doing whatever it is you were doing before, but just hold your phone by your side and try to hold it steady. Now you're just a guy that has his phone in his hand, just like lots of people that like to carry their phones in their hand. No one's going to expect or suspect that you're filming a pregnant woman, unless you make yourself obvious.
Yes, you will be shooting blind and you won't know exactly what you're shooting at the time, but it takes a little bit of practice until you learn how to position the phone in your hand correctly to get the best shot.
Alternatively, you can pretend to make a phone call while the app is filming. Launch the app, put the phone to your ear like you're making a call and position yourself so that the camera lens is pointing towards the subject. This gives you 20-30 seconds to film until you "hang up" because the other person didn't "answer". Or you can keep on filming and pretend to have a phone conversation, but then you'll be able to hear your fake phone conversation in the video.
You can also keep your phone in your pocket while filming, but make sure that the camera lens portion of the phone is sticking out of your pocket, and of course stand at an angle so that it's pointing towards the subject.

So basically, use Quick Spy Camera, hold your phone in a relatively natural position, act natural, mind your own business, and don't stand out.
I hope this helps, and I hope to see some good results soon. Any questions then feel free to ask me.

From my experience, the spy apps that don't show you any feedback (as in, turn the screen off) are useless as I always like to know what I'm shooting. Just try to position yourself in a way where nobody can see what you're recording, and that you are indeed recording. Another tip I could give you is if you're holding the phone in landscape mode (sideways) you can always pretend like you're playing a video game with your thumbs lol. Most important thing is just stay calm and keep a distance to not get spotted. The trick with "calling" someone is also pretty good, thanks Hunter