NEW YORK — The troubles with kids these days ... are not as common as they used to be. U.S. teens are having a lot less sex, they are drinking and using drugs less often, and they aren’t smoking as much, according a government survey of risky youth behaviors.

“I think you can call this the cautious generation,” said Bill Albert, spokesman for the National Campaign to Prevent Teen and Unplanned Pregnancy.

Among a decline in several risky behaviors, a sharp decline in sexual activity stood out to researchers.

The survey found 41 percent said they had ever had sex, after it had been about 47 percent over the previous decade. It also found marked declines last year in the proportion of students who said they had sex recently, had sex before they were 13, and students who had had sex with four or more partners.

The results come from a study conducted every two years by the Centers of Disease Control and Prevention. The surveys included 16,000 students at 125 schools, both public and private. Participation was voluntary and required parental permission, but responses were anonymous. Results were released June 9.

National surveys have seen a leveling off in recent years in the proportion of kids who said they had sex, after earlier declines. That led researchers to largely attribute continuing declines in teen pregnancies and abortions to more and better use of birth control.

But the new numbers suggest less sex is a factor, too. The drops are surprising enough that government officials said they’d like to see what the next survey shows to make sure it’s not a statistical blip.

If it is a true drop, the reason is not clear why. “We’re trying to look at reasons why this might be happening,” said Dr. Stephanie Zaza of the Centers for Disease Control and Prevention, who oversees the survey.

One possibility, Albert said: “It may be that parking at Lookout Point has given way to texting from your mom’s living room couch.”