Came right with guidance from various sources. Below the solution in case anyone ever wants to do something similar...
DECLARE @TempExportTable TABLE
(
Products XML,
Colours XML,
Sizes XML
)
INSERT INTO @TempExportTable VALUES
(
(SELECT * FROM Products FOR XML AUTO, ELEMENTS),
(SELECT * FROM Colours FOR XML AUTO, ELEMENTS),
(SELECT * FROM Sizes FOR XML AUTO, ELEMENTS)
)
SELECT
Products as '*',
Colours as '*',
Sizes as '*'
from @TempExportTable
FOR XML PATH('ExportList')