The emoji keyboard is included in the iOS 8.3 update rolling out today. Go to Settings > General > Software Update to download 8.3 or connect your iOS device to your computer and update through iTunes.
New flags have arrived too!
There are ~way~ more babies, as well as family options.
Just long-press the yellow faces to see more options.
Still no taco emoji, tho. 😔
But most importantly, back up your phones before you update!