When my boy was around 12, I had both a stainless steel 22 LR pistol barrel and a braked stainless steel 30/30 Win. pistol barrel for my Contender. Superficially they looked about the same. We were out shooting one day. I went into the house and switched barrels from 22 LR to 30/30 Win. and came back with the gun and gave it to my boy to shoot. I said, "you better hold on to it, it's going to kick." He, not knowing about the barrel switch said, "aw dad, this doesn't kick bad." You should have seen the look on his face when he touch the round off. The happy ending to the story; he still likes guns and loves to shoot.
As far as the how bad will a 30/30 carbine kick question is concerned, it will depend to a large extent on stock design and gun weight. I think the recoil pad area on the carbine composite stock is a bit small which will tend to emphasize recoil. Fox Ridge Outfitters sells a very nice walnut thumbhole stock for the Contender. It is a bit pricey but the recoil pad is much better. I use mine with a 375 JDJ barrel and it's not uncomfortable to shoot. It also doesn't come with studs to attach a sling so you would have to supply your own if you wanted them.