It's not necessarily unethical, but it might be unwise.
It's not necessary for you to have experienced everything you write about. Our literature would be far poorer if that was a prerequisite.
There is a risk of causing pain to those who have already suffered
However, what you're talking about is a particularly sensitive subject, and if you don't want to cause pain and hurt, you need to think very carefully about what you're doing - which you clearly are, as you asked the question.
I would ask you to consider whether this really is a good subject for you to write about, if you don't have experience of it. Good stories with these sorts of subjects are usually written by people who have experienced it, or who have worked or lived closely with people who have.
Do you know others who have suffered from child abuse? Can you get first hand accounts and tell an insightful story, rather than just repeating things you've seen in fiction and embellishing it with details that may not ring true?
If not, you risk creating something with is inauthentic and could hold up false stereoptypes which cause anguish and frustration for those who these issues affect.
Write about something you can add value to
I would recommend you back off from this subject for your first full length work. Completing a novel is hard enough without adding so many extra complications and risks.
Think about topics you do know about more in depth - where you might have insights others will find authentic and compelling. You don't have to a fighter pilot or secret agent to make it interesting.
You could write about family relationships that you do have experience of - the nuances of support and frustration. Or about friendships, their challenges and how they survive or collapse.
Whatever you decide, best of luck with your writing.