Small children are generally incapable of getting their teeth brushed alone without a lot of water and toothpaste spread about the vicinity. Also, their technique is not yet refined enough to achieve the desired results.
My youngest two are generally cooperative about this endeavor, though they might protest at first. Last night my son, 3 1/2 years, came upstairs after being put to bed, a nightly ritual. His teeth had not been brushed.
"Oliver," I said, "We need to brush your teeth."
"No. I don't want to brush my teeth today," was his certain reply.
At which point I said something like this: "Oliver, do you know what cavities are? (He shook his head.) They are little germs that get on your teeth and if you don't brush your teeth the cavities can eat your teeth all gone."
He pondered this for a moment. Seriously, watching a three year-old ponder something is the best. I could see him thinking through the consequences. This is the boy who doesn't like having his hair cut, because his fear is that it will be all gone when I am done. I could see him playing out similar consequences in his head regarding his teeth. Hmmm. No more teeth?
"Mom," he said, "Let's go brush my teeth."
And so we did.
Now, if only potty training would be as easy.