These programs scare the hell out of me. Children that young aren't ready for SCUBA. They aren't ready emotionally, mentally, physically or developmentally. I'm sure they enjoy the programs, but I doubt seriously the programs are good for them.
Children that age don't usually fully grasp there are consequences to their actions. They panic easily and quite frankly, the PADI program doesn't teach people to avoid panic. The program doesn't teach enough skills to lay a foundation which would instill the self confidence needed to avoid the fear which would prevent the fear which can lead to panic. As long as things go perfectly, your child will probably be fine, but if anything goes wrong, she's likely to panic. Panic leads to ascents while breath holding and other inappropriate actions. Such ascents are extremely dangerous in shallow water.