Welcome to Plot.ly, beautiful data representation.
Plot.ly is a fantastic data representation tool, for everything from scatterplots with regressions to box and whisker plots to pie charts. Charts are interactive when created, and you can login with Google to save your plots.
The Learn section of Plot.ly's website is particularly helpful. There you can find, under the left column that says 'web app', a tour, tutorials, and more. The tutorials on Data Analysis and Literacy, such as the What is a Boxplot? tutorial, could be useful in helping kids understand these statistical representations.