If you kill someone, that's murder.
If you kill a family member, that's still murder.
If you kill a child, that's "child abuse."
Listen up, buttercup. This joke points out how the legal system slaps different labels on the same heinous act (murder) depending on who the victim is. Killing someone? Murder. Killing your own kin? Still murder. But offing a kid? Suddenly it's "child abuse." It's like they ran out of scary words and grabbed the first thing they saw on the fridge.