I remember this being brought up once before: https://mangadex.org/thread/10110/june-2018-official-mangadex-art/2#post_61609
It seems that "borderline" is fine, as long as it's not explicitly NSFW.
If it's any consolation... for most children who are unfamiliar with such things, it's likely that any sexual connotations will fly right over their heads. For example, consider the 9 dolphins image: https://www.reddit.com/r/illusionporn/comments/1qtpyl/what_do_you_see_in_the_picture_two_lovers_most/