The first night on the ship you will be invited to the Camp Carnival room to meet the staff and receive the schedule. Since your child is only 4 she will have to be taken to Camp Carnival by you or your husband and picked up by either of you.
They have so many activities to keep the children occupied, but they are under no obligation to be there at each and every activity. That would be up to you when to take and when to pick up.
Each night you will have a "Carnival Capers" left in your cabin after the steward turns the beds down. This is the daily newsletter letting you know whats going on for the following day and times. Your child will either get one each night, or be given one for her age group the day you register her. Then you can pick and choose what she wants to do. Just plan on being flexible, children love the Camp and most kids beg to go, instead of spending the day with mom and dad. Also, a lot depends on if they make friends that are going to be there each day. Our daughter was 9 the first time she went on a cruise, we couldnt keep her with us, she planned each day with her Camp Carnival schedule and friends. Our only rule was she had to eat dinner with us each evening so we could catch up on what she did. Most nights it was like pulling teeth to get her to eat with us. She is 14, been on 5 cruises and still always goes to the first night for the "kids" or "teens" program to see who is going to be there and what is going on.
My only advise is be flexible, and plan on having a great cruise. You will love it!!