Can I ask - why would anyone do this? Several URL shortening services of the past have shuttered and it has left the web littered with links to sites that can never be resolved (linkrot) - this to me just seems like a another surefire way to speedrun future deadlinks in forums etc. Why?

Edit - I have misunderstood the assignment.

This is targeted at self-hosted/personal-domain stuff only, not general internet site URL shortening/redirection.

In addition to other advice here just be aware that Minecraft servers are prime targets for griefing and abuse.

I recommend setting it to whitelist mode and then each kid your friend wants to join just has to send their username to him so you can add the username to the whitelist. Its an added overhead but it’s much less painful than reverting to a backup for a griefed server - and your kid won’t have to worry about other kids on-sharing the server address.