To draw manga chibi well, you need to focus on exaggerating the features. Make the heads larger, the eyes super cute, and simplify the body proportions. Also, use light and bold lines for emphasis.
Luna Lovegood could be an interesting head of Ravenclaw. She has such a unique and creative way of thinking. Her love for all things strange and wonderful would make her a very different kind of head. She would encourage students to explore ideas that are outside the box and not be afraid to be themselves. For example, she might introduce new classes on magical creatures that are not commonly studied, like the Crumple - Horned Snorkack.
In fanfiction, chibi Naruto can be best characterized as a ball of sunshine. He's constantly chasing after his dreams, whether it's to be the best ninja or to get a bowl of ramen. He's not afraid to speak his mind and is very straightforward. His emotions are always on his sleeve. Chibi Sasuke is the opposite in some ways. He's reserved and a bit aloof. He values his alone time but deep down he's also lonely. When it comes to his relationship with chibi Naruto, he's slowly learning to open up. He's still competitive but in a more innocent, childish way. He's the type that will secretly admire Naruto's courage even if he doesn't say it out loud.
First, get familiar with the DC characters you want to draw in chibi style. Then, break down their complex designs into simple forms. Add lots of charm and personality. Don't be afraid to experiment with colors and shading for a fun finish.