Our bathtubs are old-cast iron with an enamel coating (like a claw foot tub, only ours are pedestal tubs) so when I get a bath ready for the boys I usually use just hot water in the winter because the tub cools the water down so quickly, until the tub warms up. I got the water in and as Noah was climbing in I said, "Tell me if the water's too hot and I'll add some cold."
He climbs in.
Noah: It's just fine.
Then I start working on getting Simon ready to get in.
Noah: It's too hot.
Me: Okay, I'll put some cold in.
Noah: My toes are too hot!!!
Me: Well, get out! Daddy's right there, he can help you if you need help.
Tim: Noah if it's too hot you have to get out right away, not wait. Hot water can burn just like fire can burn.
Noah: It can?
Tim: Yes, it can.
Noah: Well, just my toes were hot.
Well then, if it's just your toes...