First of all, Cochlear Implant is a Surgerical Option.
Cochlear Implant is part of the body, and the body is the child's body. It's his/her decision. If he/she say no, then don't. If he/she said yes, then do it.
Let me tell you story about me getting a CI.
When I was 4 years old, my parents was thinking about giving me a cochlear implant. After they talked with the doctor, they thought "Maybe we are too pressure on our child to have surgery". They feel like they should wait till I raise and make my decision.
When my parents feel that way, today I felt so very thankful to my parents for respecting my body, and who I am. I didn't twist any word in that story, my parents told me the exactly same story.
But... I choose to have a CI surgery because of curiousity. It didn't work for me at all, some people argued that I was too old for CI, that was the reason why the CI was not very benefit for me. Maybe they are right.
Maybe all of deaf children and deaf animals should get cochlear implant, and the Deaf Culture will never be here. What would you think about that?
Also, I have some friends who raised with the CI. One of my friend I am going to share.
When she was 2 years old, she got a CI. Today, she HATE her parents. Why? Her parents refuse to communicate with her through the sign (even her parents knew sign) and will treat her shit if she didn't wear the CI, also discriminate against her deaf signer friends. Somehow, she told me that she probably don't want to see her parents again because her parents kept disrespecting her as being deaf.
I didn't mean to be against you for your child to have the CI, if you think that is the best thing for your child to have CI so she can have opporiunity to have good career and good social life and good for many things. I am just saying to not forget to respect his/her deafness, and don't make his/her feel like he/she was the lower because of her deafness, and don't stop him/her from social with other deaf signers because she is learning from her true being.
Also when he/she raise to his/her teenage, he/she ask you "Why did you put me on the operation for CI?"
My advice, don't simple say "I want you to hear", it could make him/her to think that you don't like him/her as being deaf, he/she might feel overreacted.
It's better to say "I gave you the operation for CI because I want you to have varies of good opporiunity for the life". Your child might feel that you want to support him/her in any way, and it also make him/her to feel that you are giving them the freedom.
If you want your child to have CI, just don't forget to not disrespect his/her deafness.