Hi, welcome to the forum.
You could use the Core plugin's whitelist system to only allow your son and his friends to join. To set it up you can use the 'whitelist' command in the console. There are a bunch of subcommands like 'add' to add players to the whitelist and 'on' to enable the whitelist. Another possibility to configure the whitelist is the webadmin, but you'd have to configure that first. See 'webadmin.ini' for more information on how to configure it.
You could use the Core plugin's whitelist system to only allow your son and his friends to join. To set it up you can use the 'whitelist' command in the console. There are a bunch of subcommands like 'add' to add players to the whitelist and 'on' to enable the whitelist. Another possibility to configure the whitelist is the webadmin, but you'd have to configure that first. See 'webadmin.ini' for more information on how to configure it.