A child advocate (or CA) is, in its original definition, an individual who promotes the interests of children by helping to provide for their growth and protection. This definition is, however, inadequate to explain the current usage of the expression and its connotations.
Part of the difficulty is that the expression "child advocate" is entirely self-adopted -- that is to say, unlike professional terms such as "social worker" or "child psychologist," no certification or documentation of any sort is required for anyone to call themselves a "child advocate". This means that it is very easy for any individuals to call themselves child advocates, even if they have no interest whatsoever in promoting the interest of children or helping to provide for their growth. Thus, any discussion of this term must distinguish between what this expression is purported to mean, and what it seems to indicate in actual practice.
Ostensibly, a child advocate works towards the betterment of children in some specific form. Some may do so by working toward the cause of children's rights. Others may work to protect children from the harm that can arise from abuse. And others may dedicate themselves to arming parents and other important adults in children's lives with information about possible threats to the welfare of their children. In all cases, the goal of these activities is supposedly the best interest of the children.
Most child advocates, like the rest of society, are particularly hostile towards intergenerational sexuality and even those expressing an attraction to minors. The rise of online communities such as BoyChat was followed by the rise of a vigilante subclass of self-proclaimed "child advocates" who have decided the best interest of children means the eradication of those identified as "pedophiles". These individuals base their actions on the conflation of pedophilia and ephebophilia with one another, and in turn with minor-adult sex and child sexual abuse. Members of such groups (see Perverted Justice and Absolute Zero) tend to disbelieve that anybody who self-identifies with ephebophile or pedophile feelings is likely to be celibate in regard to said age-orientation.
Instead of helping children directly, this type of child advocate makes it their goal to fight against "pedophiles" online, sometimes to obsessive extremes. Such child advocates participate in "pedophile" forums as trolls, or try to out "pedophiles" who communicate online or in real life. In some cases, legal minors participating in such communities have been identified as pedophiles or potential victims of "child grooming". The distinction subjective, largely dependent upon the views of those who are targeting the minor.
In informal usage, especially on the chat forums, this term is often abbreviated "CA" (which should not be confused with El Castillo Azul, a Free Spirits chat forum in Spanish which is also abbreviated "CA").