Fear the Walking Dead is currently getting the back half of Season 2 underway on AMC, with another seven episodes left to go before The Walking Dead proper premieres.
According to The BBC, Channel 4 admitted their own internal procedures failed to catch the Fear the Walking Dead advisory, and thus nothing was done to limit its use.
(Not that Fear the Walking Dead is perfectly suitable viewing for 10-12 year olds either.)
The ASA ruled that while older children would have been fine seeing the ad, the suspenseful build-up therein could distress the younger kids.