Consent means to express a willingness to be involved in whatever one is brought to be involved in. There is no stage during human development when a child cannot express willingness or unwillingness to be involved in whatever they are brought to be involved in. It's practically a young child's job to let you know if they don't like something. If you believe that sexual activity requires some "true" form if consent that children cannot give, well you're just wrong. In order to justify treating sexual activity as something that needs a special kind of consent, it would have to be true that it is importantly different from all the other things kids are brought to be involved in. And it would have to be importantly different in some way that makes a special form of consent a relevant concern.
Children are brought to be involved in a very lot of things against their will and they are rarely traumatized for it. Sexual activity possesses no feature that makes it importantly different from all the other things they do. I'm opposed to anyone of any age or level of mental fitness being forced against their will into doing anything, but apparently, doing so doesn't result in trauma in children. But as opposed as I am to making kids do anything they don't want, I'm infinitely more opposed to causing them life destroying psychological trauma. Cultural conditioning is the only reason why something inherently pleasurable would become traumatizing. Decriminalization of pedophile sexual activities is supremely important to combating that fear conditioning. If I believed decriminalizing sexual activity with minors wouldn't result in many parents and caretakers treating sexual activity the same as they treat all the other activities they do with their children and involve them in it even if they are unwilling, then I would be delusional. Hopefully, laws which punish non-consenting sex would still be enforced in those cases, but I wouldn't count on it. But since it's true that there is nothing inherently harmful about sex and that it is instead inherently pleasurable, then that means public hate and disgust for treating it as just another activity parents do with their kids is based in moral beliefs about sexual purity. If the laws aren't about concerns of children's well-being, then they have to be about the hate and disgust people feel for pedophiles and nothing else.
In order to justify treating sexual activity with children as uniquely different from all the other things parents and caretakers do with their children, there needs to be an argument for what that difference is and why it is relevant. Everything depends on being able to argue what that important difference is. If you can't say what they difference is, then you can't win the argument.