People always tell me "I could never let my kids do what you do... I'm too uptight for that." That comment always comes funny to me as most of the people who make it didn't known me pre-motherhood to know I was a pretty tightly wound person.
I honestly don't know how people have several children and stay tightly wound.
Sure, my car use to be emaciate and I still don't like my house dirty [or my shirt, or my everything, ha.]
Yes, there is still apart of me that cringes when I hear "Can I use this for a science project?" or "Can I have some glue... I have an idea..." But the things they create, make, and learn seem to always stick out more in my mind than the messes--- because those always get cleaned up.
You can measure messes in ounces and paper towels, but you can't measure lessons learned in the here and now. Every block stacked and rope tied appears to just be a mess now, but it's the first act in a grand play of a future invention.
So---my advice---let them make a mess.
[and teach them to clean up after themselves!]