Bob-O

If fast fishin for your 7 and 8 year old grandsons is truly what your after, than I would recommend stocking 8-12" CC and a mixture of larger HB, BG, and RES. That combination will take to fish food very well and will also be very willing to bite any anglers bait.

Your stocking strategy sounds a little more along the lines of what brettski would call
10) To study aquaculture
21) A family or personal challenge to maintain a complex ecosystem