Discount only applies if the child is accompanying the parent on the same petition or application, and if the child also interviews, travels and pays all fees at the same time as the parent.
If you are filing for a CR2 or K2 visa, adjustment of status or removal of conditions separately from the parent, you will be charged the full fee for a CR1 visa, K1 visa, adjustment of status or removal of conditions.
Government fees are not discounted. Each individual child will have separate government fees.
The most accurate way to determine your exact cost is to go to checkout and select the options that apply to you.