Well you have mainly been searching for your son in your other posts and since this will be his first centerfire rifle I'd have to say one of the .22's. My daughter is nine and will be deer hunting in OK over Thanksgiving break and she'll be using a .223 shooting 55 grain TSX bullets. In the right situations and with the proper bullet I wouldn't discount a .223 as a deer and hog killer.
Since this is for your son/wife and while Tikka is a great rifle. I'd wait to buy that one in .243 Win for when your son is older. I'd pick up a Savage or Weatherby Vanguard youth model in .223 or .22-250 for your sons first rifle. Because of the way the Tikka's recoil lug is part of the stock it is harder to find affordable replacement stocks for when your son out grows the youth sized stock. The other one I really like for youth shooters is the Ruger Compact or Laminated Compact, at 6.25-6.5 lbs, 12.5 LOP, and 16.5" barrel it is youth sized and weight. However with the short barrel make sure the kids are wearning really good hearing protection as they will bark, and that can cause a flinch just as bad a recoil.