To block websites on an iPhone for kids, you can use the built-in Screen Time feature. Go to Settings, tap Screen Time, and turn it on if it isn’t already. Then select Content & Privacy Restrictions and enable it. Next, tap Content Restrictions → Web Content, where you can choose options like Limit Adult Websites to automatically block inappropriate content or Allowed Websites Only to restrict access to specific sites. You can also manually block a website by adding its URL under the Never Allow section. For better control, set a Screen Time passcode so kids cannot change these settings.