Will Starmer's under-16 social media ban actually work?

Today, with much fanfare, HM Government is rolling out its new policy to protect young people from online harms. Here is a political/legal move for which I am the target audience. I have three teenagers, and for those not so afflicted, let me tell you that keeping them from spending all day, every day goggling at one piece of tech or another is an infernal game of whack-a-mole.
Item: Child One, Instagram. Very, very occasionally, she forgets to delete her browser history and CTRL-H yields page after page after page, hour after hour, of Instagram hits. If you restrict or remove the phone app, it will be re-downloaded or the site opened instead in a browser window. My ISP used to allow an admin to block specific sites at the router, but (as I discovered after around an hour with their tech support), useless Vodafone have removed this feature. After much wrangling, I installed a third-party DNS blocker. Daughter circumvents the router by tethering a device to her mobile data.