Our daughter, getting three years old in august received her (Bi-lateral) CI in september.
I cannot describe the joy in her eyes when she recognised sounds, the thrill when we feel when she puts the CI back on her head when it falls off, the words that she now - after 10 months - starts to immitate, the kick she gets when she recognises her sisters voice calling her from the floor above (She'd sign "listen" and her sisters name.)
We are blissed with little miracles every day. It's beautifull.
We still use sign, since she started communicating with that before she got CI, but she now starts to initiate speech.
The audiologists tuned up her "sound" slowly. Apart from 2 incidents, a chair making a scraping noise over the floor, she has never been afraid or cried. Again, I think because the "power" was very low in the beginning.
But every child is different. I've heared about parents that forced the CI on the child, but imagine when you've never heared in your life. Sounds are spooky.
So, have them start off real low and your child will enjoy it.