Teens will soon have a very different experience on Instagram and Facebook. These changes to the platforms are a key component of Meta Platforms’s $18 billion settlement with 48 states to keep children safer online.Here’s a breakdown of what the new safety measures will achieve, and where they might fall short. (Unsplash)New features that will be automatically engaged on accounts of users ages 13 to 17 include daily time limits, nighttime off-limits hours and reduced functionality during school. To understand whether these changes will effectively lead to a safer experience on these social-media apps, we spoke to top legal and product executives at Meta as well as online-safety experts.Meta says the features will roll out in the next six months. Here’s a breakdown of what the new safety measures will achieve, and where they might fall short.Time constraintsEndless scrolling is a huge concern for parents, and Meta has agreed to put in place a two-hour daily limit for teens across Instagram and Facebook as well as to block the apps between the hours of midnight and 6 a.m. (Direct messaging will remain available.)Teens won’t be able to change those settings without permission from a parent who supervises their account. But the company wants to create a level playing field in the industry so that teens don’t migrate to competing apps. As part of its terms, Meta is asking that TikTok, YouTube and Snap agree to place the same daily time limits and nighttime restrictions on their apps. If those competitors don’t comply within five years, Meta will lift its limits.There is a “school mode” that mutes notifications during school hours. (Parents can loosen that restriction as well.) Teens or parents will also be able turn off the autoplay feature, which creates a bottomless video feed, but it isn’t off by default.Offering restrictions that teens can beg their parents to relax sets up a conflict between parents and children, says Josh Golin, executive director of Fairplay, a nonprofit child-safety organization. That is antithetical to the whole idea of offering default settings, he says.However, if there is no parent overseeing a teen’s account, there is no one for a teen to negotiate with.Comparisons and algorithmsMeta is automatically hiding the number of likes and reactions that teens can see on their own posts as well as on other teens’ posts. Online-safety advocates champion that change, as comparisons on social media can lead to self-doubt. (On the subject of self-esteem, teens will also now be automatically blocked from extreme-makeup filters in addition to all of the currently blocked filters.)Another huge concern for parents is what Instagram’s algorithm shows their teens. Feeds that use artificial intelligence to optimize for engagement and give priority to catchy content over more personal posts from friends and family, are often attributed to teen mental-health issues.Now, there is an option for teens—or parents—to turn off the algorithmic recommendations. But the algorithmic feed will be on by default, at the objection of safety experts.“Opting in to a non-personalized feed relies solely on teens or parents to make those changes themselves,” Golin says. “I don’t think most teens will understand what that means, let alone avail themselves of that option.”Verifications and workaroundsKids often lie about their age when they set up social-media accounts. In recent years, companies have adopted AI tools to determine the likely age of the user. If it detects users who say they are adults but are really between the ages of 13 and 17, these restrictions will be implemented automatically. Meta says it will invest in stronger technology to detect and eliminate accounts of users under 13, which are prohibited.Meta also uses various signals to determine whether the person supervising a teen account—and thereby able to turn off key restrictions, such as the time limits—is actually the teen’s parent. For example, if a parent account is created using the same device or email address the teen uses, that is a red flag.But Meta acknowledges that it doesn’t have a foolproof system for preventing teens from creating—or asking someone else to create—a fake parent supervisory account.Another longtime workaround for teens has been to create secondary Instagram accounts of which their parents aren’t aware. Going forward, parents will be notified when a teen links a secondary account, but it won’t apply to teens’ existing extra accounts.Parental controlsParental controls in general have become unduly burdensome for families as teens use multiple apps to communicate with friends. Online-safety advocates have long argued that the tech companies should simply design their products to be safe for teens.Meta’s previous move to make teen accounts more secure didn’t require parental controls, though it gave parents the ability to enable extra restrictions, such as time limits, and to monitor their children’s social connections.These new restrictions appear to up the level of parental involvement, something online-safety advocates argue will put additional risk on teens in poorer communities.“Parental controls only work in a household that has an adult with time, technical confidence, a smartphone and an account on the platform, fluency in the language the tools are offered in, and a stable relationship with the child,” says Katharina Kopp, deputy director of the Center for Digital Democracy. “Children who have all of that are usually the children who are already best protected.”Write to Julie Jargon at Julie.Jargon@wsj.com and Meghan Bobrowsky at meghan.bobrowsky@wsj.com