I didn't understand art as a kid. You need experience, culture, history, and often at least a cursory understanding of religion to understand art. Art is an expression by the artist. It is necessary to understand the milieu of the artist first.

Science is universal. It crosses time and language barriers. The underlying physical principles are immutable. Kids can be expected to understand science museum exhibits after a few minutes of explanation. You can't explain the historical and social context behind a painting in just a few minutes to a kid.