one of the things that fast growing children need that is not always in their everyday diet is iron. please correct me if i am wrong, but i have not yet found a gummy type vitamin that has iron. besides that, gummy candies and fruit leathers are not good for teeth because the sugars stick to the teeth longer than most foods, encouraging bacteria that forms plaque/cavities.
flintstones complete and other solid vitamins do contain iron and a lot of other important minerals that i don't think is possible to put into a gummy.
L'il Critters brand does have a liquid berry flavored vitamin for babies and toddlers that contains iron.