Give em linux mint, and set parental controls on the router, alternatively you can have an admin account which has a list of blacklisted ips, but i don’t really recommend that since you’ll never have a list that has everything, and if your kid wants to look at porn or whatever, they’ll find a website that isn’t blocked, also doing this probably means you won’t be able to put your kid in wheel group which imo means they won’t be able to learn as much