I am more familiar with the D3100 than D3200. I do note D3200 has higher Mega pixel count and quite a load of new nifty features. But in your case, the higher mega pixel only means more memory space wasted without noticeable performance at all.
I still believe D5100 has more AF points which helps with more accurate/faster auto focus. This is the difference between getting the shot of your kids in time, or miss the shot altogether, or the difference between a slower focus that makes your photo fuzzy (which means useless).
Your best bet is to go to a local camera store (if there is one) that you can try out both cameras and shoot people around the stores to see which one is more suitable to you. Keep in mind that it may have a lot to do with the kit lenses they come with. However, from B&H, both of them comes with Nikkor 18-55mm f/3.5-5.6G VR Lens (the same lens).
I like the D5100 for its articulate screen which helps a great deal when you want to record video or shoot from your hips.
