So if a child thinks something is "pretty" and then chooses to wear it, they're likely to experience mental issues and psychological damage?
Of course not. Ideally, I think we'd all choose our clothing based on our own personal tastes. The problem comes in when, like I said, they are aware too early of standards in beauty and the concept of sexuality. A child is very unlikely to find a bikini top specifically engineered to make her look like she had developed breasts to be pretty on that merit. Whether consciously or subconsciously, a desire for that specific function is a symptom of early sexualization.
I guess it's time to inject some sources to see if we can clear this up. Excerpts taken from an APA article (http://www.apa.org/pi/women/programs/girls/report.aspx
If girls purchase (or ask their parents to purchase) products and clothes designed to make them look physically appealing and sexy, and if they style their identities after the sexy celebrities who populate their cultural landscape, they are, in effect, sexualizing themselves. Girls also sexualize themselves when they think of themselves in objectified terms. Psychological researchers have identified self-objectification as a key process whereby girls learn to think of and treat their own bodies as objects of others’ desires (Frederickson & Roberts, 1997; McKinley & Hyde, 1996). In self-objectification, girls internalize an observer’s perspective on their physical selves and learn to treat themselves as objects to be looked at and evaluated for their appearance. Numerous studies have documented the presence of self-objectification in women more than in men. Several studies have also documented this phenomenon in adolescent and preadolescent girls (McConnell, 2001; Slater & Tiggemann, 2002).
Although most of these studies have been conducted on women in late adolescence (i.e., college age), findings are likely to generalize to younger adolescents and to girls, who may be even more strongly affected because their sense of self is still being formed.[...]
Cognitively, self-objectification has been repeatedly shown to detract from the ability to concentrate and focus one’s attention, thus leading to impaired performance on mental activities such as mathematical computations or logical reasoning (Frederickson, Roberts, Noll, Quinn & Twenge, 1998; Gapinski, Brownell & LaFrance, 2003; Hebl, King & Lin, 2004). [...] In the emotional domain, sexualization and objectification undermine confidence in and comfort with one’s own body, leading to a host of negative emotional consequences, such as shame, anxiety, and even self-disgust. The association between self-objectification and anxiety about appearance and feelings of shame has been found in adolescent girls (12–13-year-olds) (Slater & Tiggemann, 2002) as well as in adult women. [...] Research also links exposure to sexualized female ideals with lower self-esteem, negative mood and depressive symptoms among adolescent girls and women. [...] evidence suggests that the sexualization of girls has negative consequences in terms of girls’ ability to develop healthy sexuality. [...] Negative effects (e.g., shame) that emerge during adolescence may lead to sexual problems in adulthood (Brotto, Heiman & Tolman, in press).[...] More general societal effects may include [...] increased rates of sexual harassment and sexual violence; and an increased demand for child pornography.