Cuba’s Young Communist Union has been joined by Elian Gonzalez, the Cuban boy who was at the centre of an international custody battle in 2000.
Communist youth newspaper Juventud Rebelde quoted him as saying that he will never let down ex-president Fidel Castro and his brother Raul, the current president.
In its Sunday edition, Juventud Rebelde said the boy was among 18,000 people who joined the Young Communist Union on Saturday.
When he was six, Elian’s relatives in Miami lost their battle to keep him in the US. Then, in mid-2000 he was returned to Cuba with his father.
In late 1999, the boy was found floating alone in the Florida Straits. He was one of the few survivors from a group of shipwrecked Cubans, who had tried to reach the US in a handmade boat.
His mother was among those who died when the fragile craft hit a storm.
Ensued a bitter custody battle in which his relatives in Miami were backed by the anti-Castro Cuban American community there, and his father was supported by the Cuban government.
But the US courts got involved, eventually ruling in favour of Elian’s father and the boy was returned to Cuba.
Elian’s privacy is carefully guarded by the Cuban government, say BBC correspondents.