The principle is very simple -  your body needs about 10 grams of fructose a day, essentially to help glucose penetrate the cell walls so that it can be converted to energy to run the body. You can get that from two small pieces of fruit of about 100 grams each. Any fructose in excess of that goes directly to the liver where it is stored &/or converted to fat and deposited around the vital organs ["belly fat"].  Fruit juice is a particularly bad form of sugar because it's concentrated fructose - it's tantamount to drinking fat! It's not quite so bad if the fibre is not separated from the juice as it tends to ameliorate the effects of the fructose. The same could be said for whole fruit. Dried fruit is also a form of concentrated fructose and so is best avoided.

To be on the safe side, I would recommend sticking to vegetable juice and forgetting about the added fruit. And the "chewables" sound like marketing cons. The pack Nutritional Information Panel should tell you the percentage of "sugars". Divide by two to get an approximation of the fructose content. Teach the kids to like real, fresh fruit.