One of the many things that’s difficult about being a thoughtful parent is that the second you think you know what’s going on with your children, one of them throws you for a loop so big, you are nearly knocked over. That’s what it felt like when my 5-year-old daughter, Kira, smiled and told me she wanted to kill her new brother.

“What?” I asked in my sleep-deprived state. “You want to kill the baby?” I repeated, buying time to come up with a decent response. What worried me wasn’t that my daughter wanted to kill the baby. She’d get over that. What was more disturbing to me was that if I were to have chosen one of my other four children who was least likely to want to kill the baby, it would have been, without a doubt, Kira. Maternal, sweet, accommodating, lighthearted Kira. Where did killer Kira come from?

It was Kira’s 2-year-old sister, Talia, who I expected to fall apart. Talia, who was glued to my hip. Talia, who always had to sit on my lap. Talia, who fell to pieces when I left the apartment without her. Talia, whose eyes opened especially wide when anyone mentioned the baby in her mommy’s tummy.

Well, it turns out that once the baby was born, Talia had no interest in him, and a lot less interest in me.

I had gotten it all wrong. I had given considerable thought to what each of my children’s responses to this baby was going to be. And I had gotten it all wrong. I am not the only parent to have gotten it all wrong; and according to friends with older children, I will continue to occasionally get it all wrong. This is one of the many ways in which parenting is so humbling. But unfortunately, the stakes will be a lot higher as the children get older.

“I thought my daughter was one of those shy girls who didn’t have a boyfriend yet,” a mother of three said. “Boy, was I wrong. Another mother tipped me off to the fact that my angel wasn’t so angelic. And then, I admit it. I read her instant messages. I looked through her Facebook. I read her texts. Boy, oh, boy, was I wrong. Well, not entirely. She doesn’t have a boyfriend. She has boyfriends.”

This mother isn’t the only one I know snooping through her children’s cyber lives.

“I know all my kids’ passwords and I regularly go onto their accounts and see what they’re really up to,” a mother of three teenagers told me. “I haven’t relied on my instincts in a long time. If your teenagers talk to you, great. But very few teenagers really want to give their parents the lowdown.” One father of two teenagers said that for his children’s first 10 years, he had pegged his older son as the student and his younger son as the social one. “It turns out I had it all wrong,” he said. “Maybe that’s what they were like in kindergarten, but as they got older, it became clear that my younger son was really the student. Actually, it became clear to everyone but me. I think my wife and his teachers were trying to tell that to me for years and I just didn’t get it.”

Thoughtful parents know all about the dangers of pegging their children as ditzy or academic, athletic or intense. But the pitfalls don’t stop us from making those assumptions anyway — assumptions that we’re savvy enough to keep to ourselves.

“I think parents are reluctant to discuss the generalizations they make about their children,” a mother of four said. “Summing up your children in a nutshell is politically incorrect. But because you don’t want to admit to anyone that you’re writing your kid off as a space cadet or antisocial recluse, you don’t really let yourself reevaluate the situation as often as you should.”

My instincts regarding Kira’s response to the baby took into account her personality — not the reality of her going to kindergarten every day and leaving behind her increasingly verbal and adorable younger sister and newborn brother.

But like most parenting problems, Kira’s fantasy of killing the baby resolved itself. Not because I had anything brilliant to say to Kira. But, thankfully, because time — in this case, a short amount — passed. And before I knew it, Kira was cooing to the baby that he was the best baby in the world. And my faith in Kira — and, more important, in myself — had been restored. At least temporarily.

sarasberman@aol.com