When are you travelling? At what time you want to leave? Is it the only trip you’ll be making?

Without any extra information we can’t help you find the right ticket.

Ok sorry, I want to travel from Kaiserslautern/Germany to Turin/Italy on 5th of December and back on 9th of December. It's the only trip I want to make. 

Ok sorry, I want to travel from Kaiserslautern/Germany to Turin/Italy on 5th of December and back on 9th of December. It's the only trip I want to make

Your child will travel for free anyway, since he's very young. You might need a reservation for him, but that's it.

But I don't seem to find proper prices via DB, OBB, Trenitalia or SBB for the full length of the journey.  I find 215 for only a part for a single journey. I kinda doubted if an Interrail global pass would be worthwhile. But looks like it. 

But wait to buy it. Next days/weeks there will be a discount for black friday. Keep checking the interrail website next days.

Then I would just buy a 4 day global pass for you and a free one for your child. It will save you some extra money, dunno how much the discount will be though. 

If you wluld have any further questions on using the pass and getting reservations for some trains, the community will gladly help :)