To create an Amazon listings with variants such as size and color, begin by creating the required variant values in Sellware.

Then link the item to the appropriate Amazon template, making sure to use the appropriate Variant option.

If you have the ASIN ID for the children items, you can place them in the UPC field of the Variant Matrix (see image above) and simply change the macro reference field in your listing template to point to the UPC values.   (See example below)