Florida on Monday became the first state to effectively bar residents under the age of 14 from holding accounts on services like TikTok and Instagram, enacting a strict social media bill that is likely to upend the lives of many young people.

The landmark law, signed by Gov. Ron DeSantis, is the one of the more restrictive measures that a state has enacted so far in an escalating nationwide push to insulate young people from potential mental health and safety risks on social media platforms. The statute both prohibits certain social networks from giving accounts to children under 14 and requires the services to terminate accounts that a platform knew or believed belonged to underage users.

It also requires the platforms to obtain a parent’s permission before giving accounts to 14- and 15-year-olds.

In a press conference on Monday, Mr. DeSantis hailed the measure, saying it will help parents navigate “difficult terrain” online. He added that “being buried” in devices all day long was not the best way to grow up.

“Social media harms children in a variety of ways,” Mr. DeSantis said in a statement. The new bill “gives parents a greater ability to protect their children”

Mr. DeSantis had vetoed a previous bill that would have banned social media accounts for 14- and 15-year-olds even with parental consent. The governor said the earlier bill would impinge on parents’ rights to make decisions about their children’s online activities.