Samir,
For the most part, practicing on the tires you’ll be racing on will be your best bet for consistency and ease of setup. For some brands/compounds, your setup might not change much, but I know for a fact that the difference between YLCs and YLBs will probably require a little different setup, as the Bs are a little more front positive and feel like they have slightly more front grip relative to the rears compared to the YLCs. And those two are probably the most comparable of the tires you’ve listed. If you get the balance correct on one tire, the setup SHOULD be close for another tire, but there’s no guarantees. MG Yellows are quite a bit softer than the other tires you’ve listed and will probably require a fair number of chassis changes to compensate for that grip.
Besides requiring chassis changes, it’ll be tough for a new driver to be constantly switching tire compounds and having to adapt to different grip levels. It also might be frustrating to have to chase handling issues and not know if it’s because of the tires you’re using or if the kart is actually not handling well.
I would stick with the tires you’re running in the race as your practice tires. It’ll just make life easier for you and your son. The learning curve is big already. If you ask around the paddock or at the local kart shops, I’m sure they probably have a pile of used take-off tires sitting somewhere they could provide you for practice.
