Four-year-old Bennett is lounging in the over-sized cast iron bathtub, which is one of the very best things about the old log house we've been living in. His twin, Avery, decides that he wants to get in the tub with Bennett, and I hear Bennett say, "Woah, Woah, Woah! Close the door, you're letting out the stinky heat!"

It's actually something I've heard myself say, but when I say it, it's steamy heat.

Nonplussed by Bennett's orders, Avery walks into the bathroom and begins undressing, so that he can climb in. When Bennett protests, "Mom! Avery's being mean!" Avery replies with his newest favorite phrase, the linguistic equivalent of an answer, a brush-off, and a joke all-in-one. In other words, a one-liner.

"Oh, poo-poo!" he says.

It's a new thing for Avery. Unlike Bennett's stinky heat, I don't think Avery learned it from me, or anyone we know. The phrase is his own creation, and he uses it perfectly. When I say, "Avery, please pick up your sweater," or "Avery, time to put the toys away," or even, "Avery, eat your peas!" out it comes. "Oh, poo-poo!"

I don't remember the first time he said it. I'm sure that we all laughed, happy and surprised--Avery frequently chooses to use sign language, and he doesn't often speak more than one syllable at a time. Too, Avery says it in a particularly humorous way. (Unlike his brother Bennett, who's still working on timing and delivery, particularly with his knock-knock jokes, which usually go something like this: "Knock-knock!" "Who's there?" "A man! With a hat!")

Avery's timing is impeccable, and there's something inherently funny about his little cherubic face (he's about the size of your average 2-year-old) saying something so naughty (a 2-year-old with 4 years experience, as my husband Tom says.)

And now comes the hard part: Avery's had his joke, again and again. He's surprised all of us, and the neighbor down the road, and the grocery clerk at the checkout stand, and the librarian. It's all well and good, until I stop to think about it. I wouldn't allow it from my other 2 kids. Why should I allow this kind of talk from Avery?

When Avery was just a baby, and we learned that he had Down syndrome, the books about raising twins, stacked next to my bedside in a leaning tower, were slowly replaced with books about Down syndrome. I learned that for many reasons, varied and complicated, speech might be a challenge for my child.

Things like the fact that Avery's head-size is smaller, which means he has a smaller mouth, but a normal-sized tongue inside it, so there's less room to make words. Or, his smaller ears might make it more difficult for him to hear the sounds of speech. Or, the part of his brain that controls speech might be affected by his trisomy, and its biochemistry.

Despite all these reasons, it's one of the things I wanted most: I wanted to be able to talk to Avery, and have him talk to me. I figured once we could do that, he could teach me what it means to have Down syndrome, and I could finally put all the books away.

So when Bennett's first words came (mama, dada, and wow!) but Avery's did not, we began speech therapy. (Avery was about 11 months; I later learned we could have begun even sooner, and worked on things like feeding techniques and oral-motor stimulation).

We blew bubbles to encourage development of the muscles around his mouth and encourage breath control, and we sipped pudding through a straw for the same reasons. We played kazoos and harmonicas and blew party horns. We sang songs and did finger plays and learned the signs for more and thirsty and eat; play and read and sleep. We did all these things, week after week, and yet never once did I imagine the possibility of the poo-poo talk, or what I might do about it.

It's tricky, this trying to decide what is right and fair when it comes to Avery. It's like baking a cake without a recipe: how much to allow for his prematurity? How much is twinship? What about being the middle child? Adding in, of course, personality? How do you measure Down syndrome?

Which isn't, in the end, so terribly different from what we do for all our children. A mother's eye is like a prism: seeing at once a dozen versions of her child--the future, the past, the best hopes and highest potential standing right beside our darkest suspicions and deepest fears. We do what we can, trying to strengthen the weak spots and build up the good, and it doesn't always make sense to anyone else but us. I suppose that's why it's called "a mother's intuition."

I know what I need to do. I will sit down with Avery, and explain to him that "poo poo" is funny but only sometimes, and mostly in the bathroom. That he's a wonderful boy with a good sense of humor and that we can find other things that make people laugh, too. That not only do I believe this of him; from now on, I expect it.