I buy the large 2 liter bottles of the no name brand alcohol based hand sanitizer gel from Sam's or Costco.
If you have a vacuum sealer grab a quart size or gallon size bag for it, if not a regular gallon size or quart size zip lock freezer bag will do. I usually make 2 larger packs and 1 smaller pack at a time.
Pour 4 cups of the alcohol based sanitizer into each large bag and 2 cups into the quart size.
Now here is the tip- add a couple of drops of food coloring to each bag, making each one a different color. When you have an injury, it makes it easy to remember which ice pack has been in the freezer the longest.No need to mix it in, you can mix it once it's sealed. Get the kids involved and let them pick the color and smoosh it around to mix. Yes, smoosh is a word or it should be!!
Seal the bags. If you have a vacuum sealer, hit the suction button but get ready to hit the seal button as soon as the sanitizer starts to get near the edge. If using a zip lock, squeeze as much air out as possible.
Now double bag it. Put the first bag into a second and seal that bag as well. Double protection.
If after using it for a while a hole develops, just squeeze the gel into a new bag and you're back in business. The great news is that if they do leak, the alcohol just cleans up and evaporates. I've seen sites that tell how to make ice packs filled with dish soap but all I can imagine is trying to clean up even the smallest leaks and the mess it would be. I don't do mess very well.
Make sure to NEVER put any kind of ice pack directly on the skin. Ice packs should always be wrapped in a dish towel or cloth before placing on an injury to prevent skin damage.
Keep the bags in the freezer and they'll always be ready to use. These may also be used in coolers instead of ice.