Kodomo no Jikan was originally licensed for distribution in North America in 2006 by the Los Angeles–based company Seven Seas Entertainment, the first volume of the manga having been slated for an early 2007 release. According to Futabasha, the title of Nymphet was selected for the English language version at the suggestion — and later insistence — of the original creator, Kaworu Watashiya. The manga, however, soon became the target of controversy after questions were raised about its appropriateness for North American audiences. In a written statement, the president of Seven Seas Entertainment, Jason DeAngelis, observed that "those who are speaking out against Nymphet seem to be disturbed by the relationship between two characters in the story, namely an elementary school student and her adult teacher" and decided to delay the release of the manga so that he could "have an open dialogue with the large book chains and other vendors." The title was subsequently dropped as a result of these concerns, with DeAngelis saying that it was "not appropriate for Seven Seas to publish Nymphet, and that it would cancel its release of the manga."

In a second statement regarding Nymphet, DeAngelis explained some of the reasoning behind the decision to cancel the series. He stated that, "my primary reason for canceling Nymphet is due to my recent realization that later volumes in the series can not be considered appropriate for the US market by any reasonable standard." He also cited the fact that, "[the vendors] began dropping their orders left and right, so their opinion on this matter became pretty clear cut." Specifically, DeAngelis stated that, during his re-review of later Kodomo no Jikan anthologies, he discovered content that he regarded as highly unsuitable for publication. The pages cited were of a scene of the main characters, Rin Kokonoe and Daisuke Aoki, stuck in a room with freezing temperatures. The two embrace in an effort to stay warm by sharing body heat, and, in the process, Rin inadvertently rubs against Aoki's crotch, causing him to get an erection.

On June 7, 2007, Kaworu Watashiya posted a blog entry on the Kodomo no Jikan controversy in the United States. She commented that, "what I heard about 'issues in volume 2 and later' made me realize the differences in the cultures between the countries." The author went on to cite instances in later volumes that showed intimate relationships between cousins and a bath scene with a child and adult, going on to say that, "my honest feeling is, 'It's unfortunate, but what can I do?'"