Blocking Minecraft using openWrt

I have used openwrt couple of years ago on my TP-Link routers, back then I used to use it as a firewall to block p2p ports.

Now I want to use it again to block Minecraft on my local network (parenting etc.)

I have Xiaomi Router R3G at my home, I have read that it can be flashed with openwrt, has anyone had any success blocking Minecraft completely using openwrt?

Thanks.

pic of router in case:

If you know the hostnames of the minecraft servers, then it's not difficult to block them.

There are a lot of minecraft servers, it would be hard to block all of them. I used to run a private minecraft server at home for my kid. There is a default port, on which they run, but this depends on the edition: 25565 for Java and 19132-19133 for Bedrock. It might be more effective to block the default ports. But still this can be changed by the server operator. I'd advise to investigate software solutions like Microsoft Family Safety, so you could properly manage what your kid has access to and for how much time.
You are going to cave and allow your kid to play Minecraft at some point. Having the restriction on the router is much more work for you compared to allowing him/her to play via Microsoft family Safety only a certain amount of time per day or only on certain days.