Since size is a consideration and you want to play outdoors, you will probably want 1:16 scale tanks.

As you have read through some of the posts on this forum, you have probably already figured out that you can't have it all in one tank. You cannot have Smoke and sound unless you buy Hen Long tanks, but they may not work properly. []

Tamiya tanks are the best in the 1:16 scale (in my opinion) and are very reliable, but like heavyaslead stated, they are much more expensive and require a lot of time and effort to build and paint.

If your sons are anything like me and my clan, you will want to experiment with a trio of cheaper tanks to see how much interest there is after a month or two. If they are still interested, buy a set of Tamiya tanks and you will be amazed at the difference in quality, not to mention the sophisticated battles you can have together. [sm=thumbup.gif]

Good Luck!
Jason