Attach this latex tubing and leather pouch to a forked branch and you are ready to go! This is the same type of band my animal slingshots come with. The upside is it's easier to attach and potentially better for children because it's easier to draw back. The downside is that it's not as high quality as my normal replacement band.
This takes one person to attach. No stretching and tying required. It just has a loop of latex at the end. Loop over and then tug the end to tighten; like a slip knot. You can see it in the detail images of this listing.
Latex tubing is 8"