Variations

Tick the box 'is Variation' for the attribute that you need to be visible in the child item information on the listing.

For example, if you tick it for the Weight attribute then when selecting a child item (it can be a T-shirt of a particular material and therefore weight), this attribute will be visible in the description of this specific T-shirt and not just the parent item.

Keep in mind that when creating product variants, all attributes whose value will make this variant unique must be marked as variant attributes.