Older user still prefer Apple products, it is possible when these kids grow up they may switch to Apple. There is no doubt that performance of Apple products is really good and that is what people wants from a gadget.
There is no single reason for kids not having that much interest in Apple products, there are many. Google and Windows are offering attractive smartphones, tablets, hybrids, fablets, and more in different ranges and models. Kids are just trying the new offerings.