Ms. Patterson had not thought of the possibility of a draft, but her daughter said that it was all that people at school were talking about, and that many were even getting alerts on their phones with updates about the airstrike, more than 6,000 miles away. On Saturday, Ms. Patterson found herself trying to quell her children’s fears.

“We all talked about it this morning and I tried to relax them, saying there’s not going to be a war,” Ms. Patterson said on Saturday. “I like to be very, very honest with my children, but I don’t want them to worry about that. That’s for the adults right now. It’s too much for a kid to handle.”

Some young adults joined thousands of antiwar protesters on Saturday at more than 80 demonstrations to condemn the strike in Baghdad that killed General Suleimani.

At one protest in Seattle, Lukas Illa, 19, said he was not too worried about being drafted, but was concerned about the impact a war would have on others, including service personnel who might come from disadvantaged backgrounds. He also said civilians in Iran were more at risk than Americans.

“We’re not going to be affected by this as much as Iranians will be,” Mr. Illa said.

Citlali Perez, 18, of Chicago, had begun to plan how she might mobilize against another protracted war, were it to come to that.

“Mostly how I feel is scared, but also wanting to do something about it and wanting to prevent it,” said Ms. Perez, a freshman at DePaul University who has become involved in antiwar activism.