The parents of a six-year-old boy who was allegedly thrown from a viewing platform at Tate Modern have said his condition is stable, but they still do not know the full extent of his injuries.

In a statement thanking those who have donated to a crowdfunding appeal, they said: “Our son has already undergone two long and difficult operations … But he is alive, struggling with all his strength, and we remain hopeful.

“We thank you very much for your gifts and all your kind messages of support. You cannot imagine how it helps us to see so much humanity in this tragic ordeal. Thank you very much; you help us to keep going. We hope to be able to give you better news as soon as possible.”

The statement was released after the appeal raised more than €45,000 of its €50,000 target.

The family, from France, were visiting London two weeks ago when the six-year-old fell 30 metres (100ft) from the 10th floor viewing platform on to a 5th floor roof. He was treated at the scene before being airlifted by helicopter to hospital. He was left with severe injuries including a bleed to the brain and fractures to his spine, legs and arms.

A 17-year-old boy, who cannot be named for legal reasons, was charged with attempted murder in connection with the incident. A preparation hearing has been scheduled for 22 August at the Old Bailey.

At the time, the Metropolitan police said it was treating the “truly shocking incident” as an “isolated event with no distinct or apparent motive”. They said there was no known link between the victim and the arrested boy.

BBC journalist Olga Malchevska was on the viewing platform with her son at the time of the incident and described what happened as “absolutely terrifying”. She said she could hear a woman crying desperately and shouting: “My son, oh my son.”

Following the incident, the gallery closed, but it reopened the next day.