Add 1 tablespoon of contact lens solution and stir with a spoon. If the mixture is still very runny, slowly add a bit more contact lens solution, mixing well and stopping as soon as the mixture can be peeled off the sides of the bowl.
Remove the slime from the bowl and knead it with your hands. It will start out sticky, but the more you knead it, the less sticky it will feel. Once the slime no longer feels sticky, it is ready for your child to play with!
Notes
Make sure the contact lens solution you use lists “boric acid” and “sodium borate” as ingredients. If those ingredients are not listed, the slime will not form and the recipe will not work.