William Hill has admitted that the use of the image of a child and teddy bears in its Twitter ads were "not acceptable".
The tweets were brought into question after one Twitter user complained to the Advertising Standards Authority (ASA).
Three tweets were assessed by the ASA; the first showed a child jumping in the air, the second ad featured an image of two large teddy bears wearing crowns on the back of a lorry and the third featured two similar bears in front of the Houses of Parliament.
William Hill admitted its error and said it had implemented procedures to ensure the issues were not repeated.
The ad watchdog said that it "welcomed" the betting company's assurance that it had taken adequate steps to avoid a similar situation. The ASA added that the images of the large teddy bears which formed the central focus of the ads, "would have been seen as children's toys" and were therefore likely to be of particular appeal to children.
The ads must not appear again in the current form. William Hill was told by the ASA not to use images of children or images that were likely to appeal to children or young people in future gambling ads.