re: 6.5 Creedmoor

The 6.5 CM, 260 Rem and 6.5 X 55 Swede are ballistically indistinguishable when loaded to similar pressures. Compared to the 6.5 CM, the 7-08 will push a similar weight bullets to slightly higher velocities. In comparing the 6.5 CM to the 7-08 Rem, I'd score it: Advantages for the 6.5 CM
1. It's factory ammo seems to be more accurate than any other factory ammo.
2. The 6.5 CM is extremely accurate. Most of us probably aren't a good enough shot to notice the difference.

Advantages to the 7-08
1. A larger variety of factory ammo.
2. Most local stores will probably have 7-08 ammo available, but are less likely to have 6.5 CM. Of course, that's not an issue if one handloads, buys ammo ahead of time or orders online.
3. Longterm longevity. The CM is indeed VERY popular right now, but will it still be available 10-15 yrs down the road? Probably so, but no one really knows. OTOH, the 7-08's been around a long time. I don't see it going the way of the buffalo.
4. While the 7-08 has reduced recoil loads available, I don't believe the 6.5 CM does, although I'd expect it to have it at some point. W/ your son being only 6 y/o, you might find reduced recoil loads useful. I've killed 6 deer w/ a bolt action pistol chambered in 7-08 using loads that'll run about the same as does a youth load in a rifle. The loads have been very potent.

They're both FINE rounds that will kill whitetail deer equally well using an appropriate bullet and a well placed shot. Keep us updated.