I read an article recently where the writer made a point, and one I'm pretty sure I've seen made here as well, that is these billion dollar smash hit movies from Marvel can't get kids in the door, then nothing will. Anyhow, I don't want to drift the thread off topic.
In general, marketing people don't care too much for formal punctuation in situations like this, or products like this.
Hey, Kids! Comics! is the most correct. It also reads as Hey [pause] Kids! [pause] Comics! So it puts some emphasis on Kids. That emphasis is missing in Hey kids! Comics! For that reason, I like the extra comic--it's more of a call to attention.