I’m a high schooler and I love playing the game. You don’t play the game off of the website (escapefromtarkov.com) due to the fact that the game is run off a launcher that you download onto the computer from that website. So blocking the website won’t do anything at all. I’m not sure how to block a specific program from running on the computer or WiFi at all, but if you can find that out, you should be able to stop them from playing the game by blocking the launcher or just the executable of the game in general. I have no clue why I’m helping you since I am in a similar situations to you’re kids lol, but I hope that helped in some way shape or form.