So, many people like me have always wondered how to draw kawaii pictures, and just a few weeks ago i found the secret. Above is just a few of my signature bunnies, bobo, pobo, tofu, nago and coco. They may not be the cutest kawaii characters but, they all have something in common with Hello Kitty, Rilakkuma and many other characters. They do not have mouths, their heads are bigger than their body, they have no hands or feet (just a outline) and their whole character is very simple. To draw kawaii, be original, don't copy others. There are many faces/expressions used on kawaii characters such as the popular cat face :3
And yes, you can add a mouth and make there body bigger, or draw some more detailed hands and feet but i think they are the basics to achieve a kawaii look. Try different ways, there are also many Japanese kawaii characters do have a mouth.