Correct location of forward pistol grips and why?

[2HOW]

I believe the concept of the forward grip was to manage recoil and muzzle rise. Dont know why anyone would need one on an AR.  Never thought of it being a help to kids, but it may be. The farthur back on the rifle will increase stability. I hope you all have those fold up grips  That way it wont interfer with the fog light and the can opener.

[Solus]

Had a pump shotgun forearm that allowed a pistol grip to be attached at an angle to the side, maybe 30 degrees.  It did seem to allow more positive control during recoil and working the pump.  I adjusted it for the most comfortable feel during the process.

It did, however, give me the impression that I was aiming with less precision than with a normal forearm grip.  I doubt this mattered with a shotgun at Self Defense ranges though.

[WIshooter]

I have always liked a more forward grip when shooting rifle off hand.  It gives you more leverage against the muzzle end.  To see some examples of this, google for youtube videos of Magpul Dynamics Carbine, or look for vids from some top 3 gun shooters such as Bruce Piatt or Jerry Miculek. 
There are different ways to use a vertical foregrip.  Some people use them more as an index point and a stop for the bottom of the support hand.  Magpul Dynamics youtube videos might be a good way to see an example of this as well.
Everybody is different, but looking at some world class shooters and playing with different techniques might help you find what works for you and yours.

Awsome that you are teaching your kids with such nice rifles. 

[Walkeraviator]

I used to be anti vertical foregrip until i used one.  They definitely increase your control over the weapon in a rapid fire scenario.  But I agree with mounting it as far forward as you can get.  A wider stance is more controlable.

And the number 1 no-no in AR firing is putting your hand on the mag well...very little stability, and if you have a kaboom moment.... goodbye support hand.