Two children are having a blast at school, inventing new things. The boy is working on a contraption with a handle that turns in a circular motion. The girl is operating a machine with a long handle and a roller at the end. They both have big smiles on their faces, thoroughly enjoying the activity.
Considering the joyful, playful theme, I recommend coloring the children in bright, vibrant colors. The boy could be clothed in an orange and white striped shirt with navy blue pants, while the girl could be wearing a yellow dress with polka-dots or a pattern of some sorts. The machines could be painted in bright, contrasting colors - green and pink, red and blue - to add a fun element to the picture. To make the picture even more exciting, you can add stars, hearts, and other shapes in different hues.