Doesn't look like this has been mentioned anywhere (on the AA pages) so here goes....
UK APD is being scrapped (on coach tickets) for children under 12 (on day of travel) from May 2015. This will be broadened to include children under the age of 16 (on day of travel) from May 2016.
http://www.theguardian.com/world/201...ldren-scrapped