Usually when it comes to cartoon characters (I don't mean just simple designs on TV I mean any character that is drawn and appears in a drawing, comic, game, or animation), they will almost always have the same clothing and then change their outfits only for special occasions. It's a good idea to have the same outfit most of the time, since it helps with recognizability and makes it a lot easier for artists to not have to come up with a new outfit all the time.
You can however permanently change an outfit to show their growth. Kids, teens, and adults do not have the same fashion styles, so it's actually a very very ideal to change their outfit when they grow up (or else you might get jokes about their clothes magically growing with them
)