While in Japan with my Japanese wife visiting relatives, I was somewhat shocked at many of the books/magazines available. Now I'm not a naive soul and support, even commend, the Japanese approach to sex. However, magazines featuring girls under the age of 13 in swimsuits and underwear is unhealthy both for them and indeed for men (or women) exposed to such material.
My niece is the same age as many of these models and it makes me, and doubtless other men, feel very uncomfortable that we are expected, on one hand, to be paternal while allowed, on the other hand, to "enjoy" the sexualization of pre-pubescent girls. One could argue that self-discipline will conquer any feelings toward such idols or "real life" girls, but men and humans in general are weak. Hiding behind the idea that this is somehow kawaii (cute) is not the answer.
Japanese authorities should consider the implications of this for the benefit of everyone, not least the girls themselves.