What the hell does consent matter when it comes to sex with animals? They don't have a concept of consent. When a male animal tries to mount a female who's not in the mood, she attacks him and throws him off of her. That's how they get the message across that they don't want to be bothered. But if he's sufficiently bigger than her, he'll just rape her. Besides, it's a bit stupid that we worry about things like consent when you want to bang your dog but don't have an issue eating animals, with rodeos, bullfights, hunting, factory farming, animal testing, etc. It's quite ridiculous. Since when we do ask for their consent to do those things? I think non-forced sex would be the least of an animal's worries when it comes to dealing with humans. People need to stop projecting our sexual worries onto animals. Things are much more simple when it comes to sexuality outside of the realm of humans.
Also, a prepubescent child is not a good comparison to an adult animal. Animals give very noticeable mating signals when they're willing to have sex. It's different if you're comparing the child to a baby animal.