Applying Tax Calculation, individually, to child products.

[Seoirserob]

In a T-Shirt Shop . . .

When I have a child product, with a custom field plugin for size and colour, the price can be changed in the parent's custom field tab . . . or by changing the price of each individual child product.

However, my requirements are for applying a tax calculation to only one child of a parent of 5 . . . or maybe 4 children of a parent of 20.

EXAMPLE:
In Ireland there is no VAT required for the sale of children's clothing. Children's clothing is exempt, except for the largest size (XXL . . . or 12 years). So I must have ZERO tax on all child products of the parent EXCEPT for each XXL size to colour combination. It MUST be a tax calculation as customers from outside the EU will not be required to pay VAT on their purchases.

Changing the tax for each child makes no difference . . . The tax setting of the parent is applied to all child products.

Or am I wrong? . . . have I missed something?

Thanks in advance.
Rob.