You have been honest with your husband and told him from the start that you don't want children. So that's good for you. He cannot say that he didn't know that.

Rather than concentrating on all the reasons you don't want kids I would emphasize the benefits of not having them. You can mention having more disposible income, traveling, enjoying hobbies, etc.

Let him know that if he wants to be around children you will look for some kids of friends or neighbors and you can all go camping for the weekend. That might cure his itch.