Here are two simple ways to rephrase your text so a 14-year-old can understand it:
Option 1: The corn harvester and the grain harvester have small differences in their design—compare the pictures below. Rice might not be obvious in the images, so we suggest adding a farmer in the background harvesting rice stalks with a sickle to make it clearer.
Option 2: Although similar, the corn harvester and the grain harvester are built slightly differently; see the images below for a side-by-side comparison. To make the rice more recognizable, consider showing a farmer in the background cutting rice bunches with a sickle.