Hi,
Sorry to hear about your son's bike. To be honest, it's a bit of a sod of a job; not because it's difficult, but because of the disassembly it requires.
You'll need to take off the front forks, the handlebars again and remove the yoke from the bike. From there, you'll need to use some sort of punch to remove the old bearing races (have to be chiselled until they slide up the yoke) and then use a bit of PVC pipe or something to push new ones on with a mallet and a piece of work.
It's a really expensive garage job because it requires so much disassembly, expecially with removing fairings, but the parts aren't expensive; it's just tedious.
There's loads of helpful tutorials on Youtube. If you've got the bearings, I'd put aside a day to get it done if you haven't done it before.