SBObet and 188bet, who are both licensed on the Isle of Man, offer live betting on matches at Premier League under-18 level and similar matches across Europe including the German Bundesliga under-17 league. Both betting firms have a presence in the Premier League through tie-ups with several leading clubs.
SBObet are shirt sponsors of West Ham, while 188bet sponsor Bolton and Wigan and are the official gaming partner of Chelsea and official betting partner of Aston Villa.
The Professional Footballers' Association chief executive Gordon Taylor said: "It is making our youngsters vulnerable, without a shadow of a doubt. Youngsters and gambling is a bad mix, and an unhealthy one."
A spokesman for 188bet said that the company is committed to protecting "betting integrity" and stressed they were unaware of any concerns from the Premier League or PFA. The spokesman said: "A key element of our betting governance includes setting lower bet limits on smaller markets, such as Premier League Academy games, to ensure that maximum individual bets and total bet volume is not of a size that would influence any sporting outcome."