Google released a Family Link app for iOs, available in the App Store, that works on iOS 11.0 and higher. You will still need a Google account to activate the account and add your child to your Family.
Please note that your kids can always create a new google account with a fake birthday so they will get full access to the web without your permission. To prevent this situation, I suggest you try a premium parental control app like Qustodio. You can even test it risk-free before you commit with its 30 day free trial.