Child abuse? No.
But telling your kids that masturbation is evil is much more a reflection of the parents’ insecurity and upbringing. It tells me that the parent is either religiously brainwashed, or very insecure in his/her own sexuality. Why else would the parent see masturbation as evil?
The lesson to teach the kid is that there is a time and a place for everything—you don’t masturbate in public, just like you don’t do other things in public. But “evil” – that’s just nutty.
Remember that religion and religious teaching is a big culprit here too. It goes back to the “shalt not spill your seed” admonitions in the Bible, which had to do with ensuring the strength of the tribe. Every unused drop of semen was a potential warrior that was not born.
The Church grabbed onto that and made masturbation a “sin” (at least for Catholics) but for a different reason. They figure (and still do) that sperm is a human life and it isn’t to be spilled because God doesn’t like sperm wasted.
The other religious motivation is one of power and primacy. That theory goes – if you are masturbating and thinking about sexual things, then you are not thinking godly thoughts—and the church hates competition for your mindspace. So sexual thoughts are seen as a threat to the church’s supposed monopoly over your personal autonomy.
All of which is long answer to why some would say that jerking off is “evil”. But you have to look at the motivations of the people saying that.