As a way to learn some javascript, I programmed a browser-based N-body integrator. It uses a leapfrog integrator (with a small amount of force smoothing) to advance a cluster of 32 stars from their virialized initial conditions (a Plummer sphere, naturally). The integration is dressed up as a page from a fantastic children's book by Oliver Jeffers. The stars are between 1 and 10 Solar masses: massive stars are bigger. A little silly, but you can see the formation of the binaries that provide the energy to dissipate the cluster. Your child will gain a full understanding of stellar dynamical relaxation processes after 20 minutes of staring at it.