If you have booked flights for an under 16, especially as part of a package holiday for which they have been charged as an adult, you may be due a refund of the APD on their air fare. APD is payable on the flight from the UK , but the law changed in March 2016 to exclude 12-15 year olds and although only £13 shorthaul it is worth reclaiming especially if more than one child is affected.
Recently on querying this with a tour operator we received a refund on the APD paid on dd's fare on a BA flight within days. However on raising the same issue with an online booking site through which we had booked with easyjet earlier this year , we experienced much debate by phone and email before eventually getting a refund. In theory easyjet's website states that such a refund would be automatically processed after the passport information (API) is entered prior to travel, confirming the date of birth, but we were chasing this up from a flight in February. It seems these refunds, on charges which should never have been made, may not be routinely forthcoming so worth double checking.