Mountain Hardwear Mountain Goat 20°

Packs up nice and small, can be shortened, cute colors (pink for my little girl). Warm.

I like this sleeping bag. It's perfect for a girl up to the mid teens, especially if she wants to carry less weight in her pack. Warm, adjustable, well-made sleeping bag. No, you still shouldn't take your 3-year-old snow camping, but on cold nights she will be warm. I'm not sure about the durability, as it hasn't been put through the ringer yet.  

Why get a kid's sleeping bag? Two practical reasons, with one extra: increased warmth because it fits better, much less weight and better packability, and the big kicker of wife approval. This makes my wife want to go camping more often, and my daughter. And really, even when they carry their own, they will appreciate the packability.