Proper one then!
Proper Carbon steel one, or stainless? 
Top tip - If its carbon use olive oil to stop it corroding and anything edible, like fruit, he cuts with it will be OK.
Are you a good Dad? That depends, did you let him win when you played him at splits or not? 
Blessed with two daughters myself and they are both a bit older than your lad. TBH they'd be happier talking on facebook about hello kitty or whatever than wittling sticks anyway but they can both be trusted with and know how to handle pocket knives. In fact come to think about it as part of the learning process I'm sure we probably have played splits with my No. 6 Opinel during a back garden bbq at some point! - I know its always present as I dig it out the camelbak when we have a barbie 'cos its useful for slitting open the packets the burgers and stuff are in. I grew up with knives, my grandad, now dead a few years, gave me that Opinel when I did Duke of Edinburgh so I was a schoolboy - I'm now 40 and its still going strong tho now relegated to the camelbak but it was my pocket knife (literally) for years. I still carry a little keyring victorinox on my car keys and use it all the time.
Interesting thread though. Times have changed the comments above about taking his knife out anywhere public are important the consequences are serious but thats just common sense really and was even in the bad old days when I was a kid, when we could and did buy 10 inch "Rambo" style knives -the ones with hollow ally handle containing a survival kit- with our saved up pocket money from the local outdoor shop and take them down the woods to carve stuff and throw at trees, who can get closest to a knot hole in the trunk from a certain distance etc. 
We certainly never contemplated taking a knife to school or brandishing one about. Common sense and if you're not teaching your lad that then you are a bad dad.
BTW One of my mates still has his rambo knife and we used it this summer to cut some rope in the campsite at Cwmcarn. None of us gave it a second thought. Reading this thread I wonder what the consequences could have been if the heddlu had turned up looking for stolen bikes or something!
Oh and dont let him leave his opinel out on a torrentially rainy Dartmoor night. The handle swells up and its a bugger to open the thing for ages!
