You're nothing but a sexual harassment," my 7-year-old son said to his younger sister. He was responding to her description of him as a "poopie-doopie head."

Oh, no, I thought to myself. Not this. We'd already been mired in what was probably the low point of this long car trip--an annoying cascade of traded stream-of-consciousness insults. But this was much, much worse. This meant explanations and definitions and a ruling from me on the descriptive noun "a sexual harassment"--in or out of bounds?

Mom was home working, so she skipped this family trip. Now my kids were quietly awaiting my wisdom. I was on.

"Where did you hear that?" I chuckled, hinting that I found some humor in the expression and hoping that might defuse the debate.

"From Tommy. Why, is it bad?" he asked. "Can we say it?" his sister chimed in.

"Listen, there's a McDonald's up here . . ." I began. But they wouldn't be deflected.

"What does it mean, Daddy?" they asked in unison.

I worked my way through a definition (something about being mean to someone just because they were a boy or girl) and the boundaries (it probably wasn't a good idea to accuse someone of it, particularly a teacher or Grandma and Grandpa, with whom we'd be staying). Then we all pondered the event for a bit. Well, they pondered; I worried.

I always worry when they ponder something that I've said, and now I was worrying about even more: That my son's vocabulary was increasingly influenced by peers and not parents ("This rocks," and "This rots," he said repeatedly on this trip, giving me a chill). And so, presumably, was he. And my 5-year-old-but-just-moments-ago-a-baby daughter had moved from perking her ears up at the first notes of the "Barney" theme song to perking her ears up at anything containing the words "sex" or "love." She even asked me if clothes I put out for her were sexy, an adjective, it occurred to me, I don't use comfortably. Another big chill.

They still looked pretty puny as I studied them in the rearview mirror, strapped in and barely visible past the bags and boxes and coolers and suitcases and pockets full of amusements and snacks with which I'd surrounded them for two seven-hour rides. I'd have purchased that little VCR-television combination package if I could have figured out how to fit it in.

In fact, it was my inclination to constantly surround them with stuff in an attempt to preempt any possible discomfort or dissatisfaction that led to the first shock of the trip, a shock that jostled me into realizing they wouldn't be puny for long.

"Sometimes you're too nice," my daughter said seriously after returning from a Kmart visit where I'd indulged them further. And, despite her brother's subtle efforts to will her to silence (he stared at her incredulously, seeing his livelihood threatened), she went on to point out that I sometimes gave in too easily. She was right, and I wasn't prepared for her to be.

My son's turn came with the strong smell of fresh manure on a farmer's field during one stop. "Oh come on. It's not that bad," I yelled to them as they streaked to the car holding their noses and screeching. "Ew. Ew. Ew. Ew. Ew. Ew." I refused to unlock the car any more quickly and told them they were acting like babies.

"Did your dad used to tell you things like that?" my son, his fingers still squeezing his nose, snorted sarcastically and nasally as we pulled away, which added to the effect that he had become a different, more mature person--perhaps even a New Yorker. Of course my dad did, and I remember first seeing him as less than a god when he irritatingly belittled my discomfort with ice-cold, leg-aching lake water or my disappointment with a cookie ruined by coconut. I was never at ease with my own fatherhood/godliness, but I found I was unprepared for the crack in it this reflected.

That's how the trip went--steadily increasing my awareness of their growth and my need to keep up and fear that I might not. My daughter's discomfort in the men's room, my son hinting that I shouldn't be so critical of an annoying waitress. My daughter justifiably questioning my logic in one no-candy ruling and my son asking me which was worse, the infrequent beer he watched me drink at home with growing interest, or the soda I'd just refused him. My daughter examining and commenting on my clothes and my son examining and commenting on the odometer and the speed limit.

"So, are there any songs we can sing?" I said at one point, when they looked dramatically bored, like little James Deans. They looked at each other and smirked. My daughter finally suggested some songs, including one by the Backstreet Boys, whom I knew little about. And my son cheerfully named a band I'd never heard of. Enthusiasm waned and instead they talked to each other.

I watched the scenery outside moving by very, very quickly.