It could be for comical effect. Cartoons often use such actions to make the scene funny and engaging. Or perhaps it's part of a story where the sneeze leads to some kind of adventure or change.
Maybe the kid has caught a cold or is allergic to something. That could be the reason for the sneeze in the cartoon.
The reason could be that it's a visually engaging scene. The expression and the way the sneeze is depicted make it stand out. Plus, it might pique curiosity about what happens next to the kid.
Maybe the kid caught a cold or there was some dust in the air that made him sneeze while running.
Maybe the kid is sad because he lost something important or had a fight with a friend.
Maybe the kid had a long day at school or played too hard and got exhausted.
Maybe the kid caught a flu or didn't get enough rest. That could be why they look sick in the cartoon.
Maybe it's for adding some humor or creating a funny moment.
Maybe he caught a cold or was exposed to some kind of allergen.
Maybe it's just for fun or to show a funny moment of a dog. Sometimes cartoons are made to bring a smile to people's faces with such random and cute scenarios.
Maybe she's caught a cold or allergic to something in the environment.
Maybe the cat got into some dust or pollen and it made it sneeze.