David Finkelhor a leading expert on child sexual abuse has the following to say about the issue of consent.
The Issue of Consent
The ethical dimension of the problem can be approached through the issue of consent. Consent is one of the key notions around which we organize the ethics of our social interactions. As a society, we are moving toward a sexual ethic that holds that sex of all sorts between consenting persons should be permitted, but sex in situations where a person does not consent should be considered as illegal and taboo. [...] Sex between adults and children can be condemned for the same reason.
But don't many children "consent" to sex acts with adults? It is true that sex between adults and children commonly is much less coercive than rape because, in many cases, children appear to consent passively or even cooperate. If we say that sex id "Okay" if consent is present, doesn't this legitimate much adult-child sex?
The key argument we make is that children are incapable of truly consenting to sex with adults because they are children. For this reason, sex between an adult and a child cannot be sanctioned under our moral standard, which requires that consent be given. However, to make this statement, a more detailed discussion of consent is necessary.
For consent truly to occur, two conditions must prevail. A person must know what it is that he or she is consenting to and must have true freedom to say yes or no.
Can children fulfill these conditions in relation to sex with adults? It is fairly evident that they cannot. For one thing, children lack the information necessary to make an "informed" decision about the matter. They are ignorant about sex and sexual relationships. It is not only that they may be unfamiliar with the mechanics of sex and reproduction. More important, they are generally unaware of the social meanings of sexuality. For example, they are unlikely to be aware of the rules and regulations surrounding sexual intimacy - what it is supposed to signify. They are uninformed and inexperienced about what criteria to use in judjing the acceptability of a sexual partner. They do not know much about the "natural history" of a sexual relationship - what course it will take. And finally, children have little way of knowing how other people are likely to react to the experience they are about to undertake - what likely consequences it will have for them in the future.
Children may know that they like the adult, that the physical sensations feel good, and on this basis may make a choise. But they lack the knowledge the adult has about sex and about what they are undertaking. This "ignorance" stems from the very fact of being a child and inexperienced. In this sense, a child cannot give informed consent to sex with an adult.
For another thing, a child does not have the freedom to say yes or no. This is true in a legal sense and also in a psychological sense. In a legal sense, a child is under the authority of an adult and has no free will. In a more important psychological sense, children have a hard time saying "no" to adults, who control all kinds of resources that are essential to them. Food, money, freedom all lie in adults hands. In this sense, the child is like the prisoner who volunteers to be a research subject. The child has no freedom in which to consider the choise.
This lack of freedom is especially true when the adult propositioning the child is a parent or a relative or another important figure in the child's life, as is so often the case. Most of what we see as "consensual" behavior among children is a response to the powerful incentives and authority that such adults hold. As one of my interviewees said, "He was my uncle. He told me what to do and I obeyed. I was taught to obey adults." Thus a child cannot consent, in a moral sense, to sex with an adult because a child is not truly free to say no.
[...]
A somewhat analogous situation, I think, is that of sex between therapists and patients. Many patients may benefit from sex with their therapist, but the argument that such sex is wrong does not hinge on the positive or negative outcome that results. Rather it lies in the fundamental assymmetry of the relationship. A patient, I would argue, cannot freely consent to sex with a therapist. The main consideration here is that, in the context of a therapeutic relationship, a patient is not really free to say yes or no. Even if the patient liked it, a moral wrong would have been committed.
[...] Is a secretary being propositioned by her boss truly free to refuse? In many cases, no. Full consent is not present in all adult-adult encounters. Some adults probably deserve protection along with children. However, the greater potential access that adults have to both knowledge and freedom puts them in a different category. Children constitute a clearly identifiable class where these conditions do not prevail; they deserve special protection.
Second, some people argue that the notion of "inability to consent" involves an oppressive type of paternalism. Most of the new champions of eliminating so-called "age-of-consent laws" have made their arguments on behalf of the "rights of children," such as the right of children to express themselves sexually and choose whomever they wish for sexual partners (O'Carroll, 1980; Presland, 1981). It may be true that children are opressed by arbitrary adult-imposed controls. But it seems extremely doubtful that any large group of children are complaining that they are not "allowed" to engage in sex with adults. If polled, we suspect children would vote for better protection against adult sexual overtures, not more "freedom."
These self-proclaimed children's liberationists tend to minimize two parts of the problem. They do not truly believe that adults are vastly more powerful than children. They think, for example, that the fact that the adult badly wants the child to like him, or the fact that the child's disclosure culd put the adult in jail, really equalizes the power imbalance that exists between an adult and a child. They also do not acknowledge the enormous manipulativeness and callous lack of regard for children's well-being that characterize the behavior of many persons who try to seduce children. Most children are not capable of protecting their own interests in the face of this power and this guile (Gay Left Collective, 1981). There is nothing wrong with paternalism where it provides children with protection they need and cannot give themselves.
Child Sexual Abuse - Chapter 2: Sexual Abuse as a Moral Problem
David Finkelhor
The Free Press, New York, pp.14-22, 1984