That is really a personal preference. I like deep pools myself, even if I am not diving, I like the deep end. So I vote for the deeper the better.

If your kids are good swimmers and always have adult supervision (which they always should), you should be fine with any depth. If you want a pool that they can walk around in, then you might want a shallower pool. It is really up to you how you want to use it.

I have a 9' deep pool, I have kids (not mine (relatives and friend's kids)) that are around the age of your kids and younger, they do swim in the deep end of my pool, they are really good swimmers and divers.

When I have friends over that have kids who are not very good swimmers, I rope off the deep end.

I personally wouldn't mind if my pool was deeper than it is.

I think you need to ask yourself what it is you want out of the pool, what will it's purpose be? Since you wont be diving/jumping or sliding, the depth really doesn't matter much. Unless you want to play water polo in a pool of regulation depth.

From my experience, kids love to jump into pools, shallow pools are not safe for jumping into. I also believe that if you want to allow jumping in, you really need a diving board or diving platform. It helps to tell people where it is safe to jump or dive. I am not suggesting that you need to allow jumping or diving though.

On the other hand, pools of any shape, size, depth are just fun.

Just my thoughts.