> . If a little get (well below the age of reason) reaches for the pretty red glowing burner atop the stove, you slap away his hand because the small pain of getting his hand slapped will serve to make a second attempt less likely

No, you don't; if they are well below the age of reason, they are well below the age at which they will connect the hit with the reason for it.

That's why you don't let kids that young around a stove in the first place, and if they do get loose around one, you restrain and remove them. This may involve incidental pain, but not intentional, instrumental pain.