1. Start by combining the fruit juice and gelatin in a small saucepan over low/medium heat, stirring well to combine. This usually takes only a minute or so until the gelatin is dissolved completely. Remove the warm mixture from the stovetop.
2. Group 20 to 30 wide-mouth straws in a bunch, securing them with the rubber bands until they cannot move. In a large glass or jar, pour about 2 to 3 tablespoons (30 to 45 mL) of the juice mixture into the bottom. Now place the banded straws into the Mason jar so the juice mixture can fill the very bottoms of the inserted straws. Make sure the straws are vertical or the "plugs" will not form in the bottom of the straws—this is a necessary step before moving forward.
3. Now refrigerate the straws and Mason jar until the bottom gelatin is set, anywhere from 10 to 20 minutes. Place the remaining juice back onto a warm burner so it does not set in the saucepan.
4. Pour the remaining juice mixture into the straws, distributing evenly. You will want to leave a little space at the top of each straw to allow for easier removal. Refrigerate once more for about 30 minutes (sometimes longer).
5. Pull the straws out of the rubber bands and briefly run them under warm water. Pinch the straw from the end with the space and begin squeezing the "worms" out the other end.
To store, place them in an airtight container like a resealable bag so that they are not exposed to air (or they will dry out). The worms can last up to a week refrigerated.
For little hands: While supervised, your child can help whisk the gelatin into the juice and pour the mixture into the straws.