We (meaning, everyone) talk about children as if they are some other species. They are us and we are them. It is not like being man or woman. It is no immutable characteristic, just a life-stage. If anyone wants to know anything about children, they should just ask themselves. When we talk about children, we really should not say ¨They are [like this]¨, we should be saying "I am [like this]". The differences between adults and children are only individual differences between particular adults and particular children. I have found this incredibly odd that we talk about ourselves as if there is some insurmountable divergence between whatever generation we belong to and those younger than us. There isn't.
I remember being a child, does anyone else? (In retrospect, I impress myself. I am amazed at the depth and profoundness of my thoughts. Although, none of those thoughts were sexual...)
As for the question about whether children can consent, it depends on the sex of the child. Girls and boys are not in any way similar. Apart from that, we should talk about consent as it relates to us at that age - not others because there are no "others". The question, in my opinion, is not "can children consent?", but rather "could we consent when we were children?". In order to answer that question, we must be prepared to explore the honest answer and face the truth regardless if we like it or not.

As for the test, excuse me for being blunt but it is stupid. For one thing, a child 100% understands what candy and money is, but they do not understand the concept of sexual intercourse or the emotional and physiological consequences of it. Little girls can't even conceptualize what their internal genitals are. Adults can tell them, but it is so far outside their realm of experience one might as well be reciting a cooking recipe in Chinese (to an English speaker).
There are other reasons the test fails to prove anything, like a child's difficulty with language and limited vocabulary. They do not KNOW what to say or how to say it. They have limited ability to express themselves verbally. But there is another thing...unless an adult is massively lacking in self-awareness, an adult generally has some understanding if he (or she, I suppose) has used any manipulative tactics. The adult would probably be able to tell if his own actions had coercively elicited verbal consent.
I don't mean to attack you or your ideas. I'm glad your thinking about it and it is an interesting point of discussion. I just don't think it works AT ALL in it's current form.