Charles is regarded as one of the smallest in class, tying with Nora. He has a slightly chubby body with light grey fur. His inner-ear, hands, tail, feet, and muzzle are pale pink. He has black eyes.
Charles is a friendly but very withdrawn mouse. Due to being so shy, he sometimes struggles when it comes to approaching others or speaking up, until he gets to know them. He enjoys typical boy activities, such as pretending to be an astronaut or a plane flyer. He doesn't really seem to like sports as much as the other boys though, and when he gets to know someone, he can be very kind and sweet to them.
Charles generally wears a red shirt with blue overalls.
Charles is very kind with Lily and is implied to be a really good friend of hers. He helps her find missing items and tries to be patient with her, since he knows she can't really help it. In the Valentine episode, he made her a special Valentine.
Sometimes Charles is seen playing or hanging out with Nora. They are able to relate due to their species and small-stature. However, while Charles is reserved and quiet, Nora is very bold and loud.
Charles is good friends with Doris, whether he enjoys her abstract paintings or stands up to her brothers for her when they call her a shrimp.
Charles and Yoko are both somewhat quiet amongst their friends, so they usually seem to be in friendly terms and enjoy playing together every so often. They both like to play Go Fish.
Charles is shown playing with Timothy a fair amount of times in the series, most-likely due to minor shared interests. In fact, this includes times when Yoko can't come over to play with him due to ballet classes.
- Charles is one of the few characters to have someone outside of his family home to appear. This being his aunt, who came by to visit when he was getting ready to go to school in one episode.
- In his original book, "Shy Charles," he did not speak at all.
- Charles likes Mount Fuji drops.
- Charles is the only student at Hilltop School to always wear pants (Timothy only wore overalls on the first day).