Hi, I'd like to help you with your question.
It depends on the age of your child and their level of understanding of what is going on. Most likely, until your child is old enough to talk about how they feel about their father and the situation he is in, you may be ok with finding other ways to have your child communicate with his/her father.
If your child can understand the situation yet, explain that Daddy is away for a while but will be back. If the child's father is involved and cares about the child, have them communicate by letters. Read the letters to your child from their dad and explain that Daddy loves them. Have you child draw pictures for their father and also take pictures of them to send. If they can, have them talk on the phone with their father also.
If their father is going to be in prison for a number of years, as your child grows, be sure you answer questions honestly but at the child's level. Keep reminding them that their father loves them and would be home if he could be. Also, involve your child with their father's relatives so they can get to know one another and hear stories about their father.
Consider counseling as your child grows and begins to understand what is going on. Also, once your child is old enough to give an opinion, ask if they want to go see their father. They need to have a choice either way. If they do not want to go, assure them that the choice is ok and that dad understands.
There is also a book that may give you more guidance about your choices. It is called Loving Through Bars: Children with Parents in Prison by Cynthia Martone. Amazon.com has it available or try your local library.
I hope this has helped you,