I have a Kid Reel, great for towing on foot, but takes a bit of skill when on a bit. https://www.kidreel.com/
You need a hand free to pull it (unless you fashion a hook for the handle), there were talks that Kid Reel were going to release something in the future. Grabbing the handle whilst on the bike riding is difficult (might be due to how small my daughters bike is and the distance to reach down).
It isn’t elastic, so there can be a jolt when it is fully extended.
So not perfect, but the bit I really like is the easy release (which I control rather than the kids), just get close to them, let go of the handle and it safely goes back into the reel. Means no stopping at the top of the hill, just keep riding.