WHAT THE FUCK

He was referring to the “Child” in the black cape not Dandy since he was not yet or age 15

The child in the black cape was 15 tho. Because children aren't sent back to palace until they're 15

Yes which makes sense because the said “And the child had just bloomed” or something like that so he’s obviously talking about one of his Children in the black cape

I second that. He mentioned that the child had just bloomed, which I assume is an euphemism for defloration. It is quite likely the "child" in the black cape that he brought into his chambers of bloom. Leaves a sour taste in your mouth still that the King thinks so little of his son.

I think he's referring to dandy since the black cape kid was fed to the dog. I don't think that'd bother him

It would bother him. Notice that the only times the King ever changed his expression to something other than boredom is when it concerns his "children" (with the capes)? His reaction to one of the children dead is akin to a child finding out that his toy broke. He doesn't give two shits about his sons. I'd give more examples but that would be spoilers so....

Yeah but he let the dog loose on the caped kid, he was dead before dandy. He probably kills them after sex like that kid with the birthmark that Theo saw. Well maybe the spoilers tells a different story.