Here is a video of Jack Jack quacking. This is his bark which is generally reserved for: 1) I'm hungry and 2) Dreaming and waking himself up! If you notice he just puts his whole little body into it!
My wife was making breakfast for them and Jack has a tendency to get really impatient when it comes to meal time.
By the way, yes, I was speaking baby talk to them, I normally don't sound this way. haha.