We look forward to meeting you and your son in game. It sounds like you did everything just right.
Unfortunately, currently Mojang's authentication servers are down. That's where your account's username and password must pass through before accessing any public server. This is not an issue with Famcraft, but with Mojang's services. These little outages do not usually last too long. Hopefully you will be able to log in soon.
You can keep an eye on the Mojang authentication server status here:
xpaw.ru/mcstatus/ Thanks! And welcome to the Famcraft forum.