Dozens of Alfie's supporters gathered at Springfield Park, next door to the Alder Hey Children's Hospital in Liverpool, after the news of his death.
Mourners could be heard chanting Alfie's name, as well as crying and consoling each other, before the balloons were released into the sky around 3pm.
James, 20, posted a message on social media thanking everyone who supported the family through Alfie's illness and court fight.
Alfie's case received much attention outside Britain, especially in Catholic countries.
Doctors overseeing Alfie's care in the city of Liverpool said further treatment was futile and not in his best interests, and that he should be allowed to die. Alfie passed away at Alder Hey Children's Hospital after he was put on life-support in 2016. Alfie's parents appealed the decision, only to lose that appeal and watch the Supreme Court dismiss the case. The parents disagreed, and his case was referred to the Family Division of the United Kingdom court, only for the court to rule in favor of the hospital.
Alfie's parents have been backed by Pope Francis and Poland's President Andrzej Duda.
The Pope added: "Today I pray especially for his parents, as God the Father receives him in his tender embrace".
Gemma Lowery wrote on The Bradley Lowery Foundation Facebook page: 'So sad to hear about the attractive Alfie Evans I'm sending all my love to Alfie's parents, they did everything they could for their little boy.
INSTAGRAM•ALFIESARMYAlfie Evans latest news update A
The death came after an easing of tensions between the family and the hospital.
During the legal dispute, the couple had criticized the hospital fiercely, and Thomas Evans described his son as a "prisoner".
A statement from Alder Hey Children's Hospital in Liverpool, where Alfie was treated, said staff expressed their "heartfelt sympathy".
The incident itself has caused incredible amounts of public outrage and campaigning for better treatment, with the hospital staff reportedly shocked after countless acts of abuse towards them.
"Our little family along with Alder Hey has become the centre of attention for many people around the world and it has meant we have not been able to live our lives as we would like", he said.
Alfie's parents, Tom and Kate Evans, had been in a constant battle with the courts to overrule and keep their son alive. "This has been a devastating journey for them". Pope Francis met with Evans and appealed for the wishes of the boy's parents to be heeded, saying only God can decide who dies.
Supporters of the parents staged angry protests regularly outside the hospital and tried to storm the entrance at times.
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