Putting lemons or oranges in water flavors it. Stevia is a natural, calorie free sugar - but there are varying accounts on this in terms of safety. I use it myself, sometimes, and think it's way better than regular artificial sweeteners. I don't know about drinking it daily, in large quantities, though.
Could you just give your kids real juice instead? They have some organic, sugar free juices that are very tasty.
Otherwise, you can always say "Jay juice" is for grown ups. I actually think artificial sweeteners should fall under the "grown ups only, use at your own risk" labels!
There are a lot of things that you can mix with water to make it taste better that are sold in health stores. Hemp powder comes to mind. Chia seeds - though tasteless, do add fun/interesting texture to the water.
First special delivery - April 2010 :