The interview went well and we were able to add the child on the day of the interview. However, we could not get visa for the child because we didn't have his medicals ready. So, we were told to go and do his medicals and then schedule an appointment on ustraveldocs website. Right now, we are just checking the website daily for interview dates to open up.
If you are in the similar situation, a lot of things could have been done differently because we realized a lot after the fact. When you inform them you have a Child you want to add, they will create an account for you on ustraveldocs where you should go and update your profile. Make sure you add your child under dependent and he or she will be linked to your case number and then you will be able to do his medicals prior to the interview date. That was the major step we missed that didn't allow us to do his medicals prior to the interview because he wasn't linked to the case number.
You will not get visa for him if you don't have his medicals prior to the interview date. Once you do that, you will be able to make the IV fee payment at the embassy on the day of the interview.
Let me know if you have any other question or need any clarification.
Wishing you all the best!