The Advertising Standards Authority investigated after receiving three complaints about the ad, which was shown twice, at 5.35pm and 6.40pm, on 10 April this year.
Channel 4 told the watchdog it had discussed whether the ad should be shown during the film with Clearcast, and were advised that while it had a dramatic tone, there was no graphic content which would warrant a restriction.
But the channel overlooked a "presentation code 32" recommended by Clearcast that advised broadcasters to view the ad to determine whether it was appropriate to be shown during programmes appealing to children under nine.
Channel 4 said its internal system had failed to spot this, and apologised for any distress caused.
After receiving three complaints, the ASA ruled that Channel 4 had breached BCAP Code rules on children and the scheduling of TV ads, and ordered it to make sure in future that ads with the potential to distress younger children were scheduled sensitively.
