Everyone needs to own a 22 Long Rifle. They provide great fun and practice for shooters of all ages and skill levels whilst being affordable to shoot. They also provide an excellent platform to teach and reinforce gun safety.
A 223 or even a 243 is great for youth hunters. You will need to asses the shooter's limits and avoid placing them in a situation that exceeds their abilities.
Either of these cartridges or even larger calibers can be rapidly tamed with a decent muzzle brake
For the type of practice you describe, I would think that you're not necessarily trying to minimize the effects of wind with the ultimate long range rifle. Rather, you're looking for an opportunity to learn to read wind and correct appropriately and measure your progress over time.
As such, these small cartridges are often very accurate which will allow you to attribute changes in POI to specific conditions such as wind while comparing to your ballistics software.
As you gain confidence, your 300 wsm
has the potential to be an effective LRH rifle. With a good muzzle brake, you might be surprised how soon your kids would be able to shoot it accurately. Nonetheless, starting slow and working up will pay dividends down the road.
Good luck and hope this helps.