Federal definition of child pornography:
18 U.S. Code 2256 - Definitions for chapter LII Legal Information Institute
"(A) Except as provided in subparagraph (B), “sexually explicit conduct” means actual or simulated—
(i) sexual intercourse, including genital-genital, oral-genital, anal-genital, or oral-anal, whether between persons of the same or opposite sex;
(ii) bestiality;
(iii) masturbation;
(iv) sadistic or masochistic abuse; or
(v) lascivious exhibition of the genitals or pubic area of any person;
(B) For purposes of subsection 8(B) [1] of this section, “sexually explicit conduct” means—
(i) graphic sexual intercourse, including genital-genital, oral-genital, anal-genital, or oral-anal, whether between persons of the same or opposite sex, or lascivious simulated sexual intercourse where the genitals, breast, or pubic area of any person is exhibited;
(ii) graphic or lascivious simulated;
(I) bestiality;
(II) masturbation; or
(III) sadistic or masochistic abuse; or
(iii) graphic or simulated lascivious exhibition of the genitals or pubic area of any person;
(8) “child pornography” means any visual depiction, including any photograph, film, video, picture, or computer or computer-generated image or picture, whether made or produced by electronic, mechanical, or other means, of sexually explicit conduct, where—
(A) the production of such visual depiction involves the use of a minor engaging in sexually explicit conduct;
(B) such visual depiction is a digital image, computer image, or computer-generated image that is, or is indistinguishable from, that of a minor engaging in sexually explicit conduct; or
(C) such visual depiction has been created, adapted, or modified to appear that an identifiable minor is engaging in sexually explicit conduct. "
Kissing is not "sexually explicit conduct or material."
Old Sears catalogs had minors in underwear. Just because a pedophile may have used those as erotic material, doesn't make the material pornographic.
A relevant example in law:
"Correspondingly, the government contends that Amirault's admission that he obtained the photograph because he found it erotic amounted to a concession that the photograph is sexually explicit.
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We believe, however, that it is a mistake to look at the actual effect of the photograph on the viewer, rather than upon the intended effect. See Villard, 885 F.2d at 125. If Amirault's subjective reaction were relevant, a sexual deviant's quirks could turn a Sears catalog into pornography. See id.; Wiegand, 812 F.2d at 1245 ("Private fantasies are not within the statute's ambit.").
("When a picture does not constitute child pornography, even though it portrays nudity, it does not become child pornography because it is placed ... in a forum where pedophiles might enjoy it.") (citing Faloona v. Hustler Magazine, Inc., 607 F.Supp. 1341, 1354-55 & n. 44 (N.D.Tex.1985))."
173 F.3d 28
Stands out in my recollection being the first. 
