If you were genuinely concerned, you could always ask them how they made it, and if anything seemed fishy The number of cases of food poisoning in the US food

If you were genuinely concerned, you could always ask them how they made it, and if anything seemed fishy The number of cases of food poisoning in the US food service industry each year leads me to believe that it's not so easy to detect contaminated food sources. And yes, you can buy a cup and throw it out, but we're really back to asking what lesson you're teaching. I maintain you're teaching "be cute, get handouts, ignore costs" early with a lemonade stand.