Elian Gonzalez sent a note Sunday wishing a speedy recovery to "my dear grandpa Fidel," and Cuba's vice president said the world's longest-serving leader is recuperating well after surgery.
Former Nicaraguan President Daniel Ortega arrived in Havana, telling Cuban state media, "I am sure that we will soon have Fidel resuming his functions and leading his people."
Gonzalez, the Cuban boy at the center of an international custody battle with family members in Miami six years ago, published a letter in the Communist Youth newspaper Juventud Rebelde signed with "little kisses" from him and his half-siblings and cousins.
"We send you this letter to let you know that we are worried about your health," Elian, now 12, wrote. "We hope for your speedy recovery and take the opportunity to wish you a happy birthday, may you have many more."
The ailing leader turns 80 on Aug. 13.
Vice President Carlos Lage said in Bolivia Saturday that media reports that Castro had abdominal cancer were false.
"He is coming along well. He does not have stomach cancer," Lage said. "He's been made well by the operation and is recuperating favorably."
Lage's comments were the most detailed by a Cuban government official about Castro's medical condition since Monday, when it was announced that Castro had undergone surgery for intestinal bleeding and temporarily handed over power to his brother Raul, 75.
Havana has provided no details and released no pictures of Castro — fueling speculation around the world about his condition. Raul Castro, the defense minister, also has not been seen in public since the announcement.
Cubans were told Tuesday in a statement attributed to Castro that most details of his health would be kept "a state secret" to prevent the island's enemies from taking advantage of his condition.
Authorities have been calling on Cubans to reaffirm their commitment to Castro and the government, and have beefed up security by mobilizing citizen defense militias, increasing street patrols, and ordering decommissioned military officers to check in at posts daily.
The enemy in Cuba is perceived to be the U.S. government and hardline Cuban-American exiles. President Bush's call Thursday for democratic change on the island was seen as a provocation.
Washington insists it is pushing for peaceful change in Cuba and has no intentions of invading, with White House press secretary Tony Snow dismissing as "absurd" the suggestion that the United States would attack.