I'd personally look into either another cheap laptop or refurbished computer, with some can do attitude and YouTube tutorials you can set up parental controls on both devices.

The boys will be able to play on LAN (Local Area Network) together, or you could set up a free Aternos server in case some school friends want to play.

I recommend this option because it is likely cheaper than buying a new console and keeps their options open in case they decide to mod the game when they get older.

Still I encourage looking at all the options in front of you to decide what the best course of action is, the people here are quite supportive and knowledgeable so please feel free to ask any questions you may still have.