We all have those days even if we aren't parents, that we end up misplacing a bottle with something other than water in it. When you finally find the bottle it's all gross with mold. I'm guilty of just tossing the bottles and buying a new one at that point. But if you've found yourself with one of these bottles, try to soak the bottle with a teaspoon or so of Clorox bleach, and then fill the container 2/3rds full of water.