Lemonade stands

One of my kids and his friend really want to do a lemonade stand (or something to that effect) this summer. I'm not really liking the idea of selling actual lemonade but I was thinking maybe they could stuff some freezies in a cooler and walk over to a local dog park. A big part of me wants my kids to actually execute an idea rather than dream about it and not actually do it. I want them to learn about money to some degree and maybe learn some lessons about making money... potato quality clip from my favourite show

Did you ever do a lemonade stand (or similar) as a kid?

What are some other things they could sell that would actually work?

Would ice be enough to keep freezies cold or should I buy some dry ice?

Is this all a dumb idea?