Laptops don't have video inputs, connect the pi to his tv.
You can have your son sign into his minecraft account and then you can download and install it again at no charge. Get the PC edition, not the win10 edition.
If you didnt mess with the harddrive then it will find his old saved games no problem. If you need to find them and move them to a new pc they are at c:\user\Username\AppData\Roaming\.minecraft\saves (yes there is a dot in front of minecraft) You will need to set your filemanger Folder and Search options (under Organize) to view hidden and system files. Each folder in the Saves folder is a separate minecraft world so copy the whole folder or just copy the whole Saves Folder.