You mean the reduction of APD for the under 12's and later the under 16's?
You'll get this refunded if you paid for the flights before it was announced otherwise it should have been adjusted for new bookings.
If you mean the merging of APD Bands C and D into Band B was known about more than a year in advance so unlikely you would have been charged the old higher rate in the first place.
EDIT - found this on the VS website re Childrens APD
http://www.virgin-atlantic.com/us/en/tr ... pdate.htmlBUT note that it only applies to Economy.