West Ham gambling sponsor Betway has been fined £400,000 by the Gambling Commission for marketing on the kids' section of the club's website.
West Ham were one of seven clubs with links to betting sites from children's pages, which break regulators' rules.
But the commission could not confirm if action would be taken against them.
The clubs included Premier League sides Arsenal, Tottenham, West Ham and Aston Villa, plus QPR, Millwall and Reading from the Championship.
Betway was fined a total of £408,915 for also having the firm's link on West Ham's 'Young Hammers at Home' webpage.