This brief video from Crash Course Kids introduces students to the difference between weather and climate. The video focuses on the weather and climate of Yuma, Arizona. Students can analyze data averaged over years to determine if the weather shown in the video in Yuma is typical of the climate. Climate data may be found here: http://www.usclimatedata.com/climate/yuma/arizona/united-states/usaz0275
Although the term average is not typically introduced in third grade math, students will often be able to come up with a useable definition, such as typical, common, or expected. The expression, "Climate is what you expect; weather is what you get, may be helpful to students as they develop their understanding of the two related terms.