Supporters of Connie Yates and Chris Gard will deliver a petition of more than 350,000 signatures on Sunday calling on doctors at GOSH to allow the baby to travel and receive experimental treatment.
In a series of tweets on the @charliesfight Twitter campaign account on Saturday, the family thanked supporters for sharing the story of their 11-month-old son worldwide.
A HUGE thank you to all you out there supporting and sharing Charlie's story!please keep going!the fight is not over!!!! #charliegard
— Charlie's Fight (@charliesfight) July 8, 2017
The couple, both in their 30s and from Bedfont, west London, want to take the baby to a hospital in the US for experimental treatment, but lost a lengthy legal battle after judges ruled in favour of doctors at GOSH, who argued the therapy would not improve Charlie's quality of life.
The family were joined by an American pastor who travelled to the UK to pray at Charlie's bedside and tweets from the campaign account suggested he had initially not been allowed on the neonatal intensive care unit, which also cares for other seriously ill infants.
But Patrick Mahoney, a pastor at the Church on the Hill in Washington DC, later said he had been able to pray "for a miracle" alongside the parents.
So now Great Ormond Street Hospital won't allow Rev. Patrick Mahoney, pastor, to pray at the #charliegard 's bedside? #SAVECHARLIEGARD pic.twitter.com/oyUzAj5ffR
— Charlie's fight (@Fight4Charlie) July 8, 2017
GOSH said on Friday it had applied to the High Court for a fresh hearing "in light of claims of new evidence relating to potential treatment for his condition".
The decision was prompted by claims of "new information" from researchers at the Vatican's children's hospital.
Clinicians from the Bambino Gesu paediatric hospital's neurosciences department said tests in mice and patients with a similar, but not the same, genetic condition as Charlie had shown "dramatic clinical improvements".
Charlie inherited the faulty RRM2B gene from his parents, affecting the cells responsible for energy production and respiration and leaving him unable to move or breathe without a ventilator. The therapy is not a cure.
GOSH describes experimental nucleoside therapies as "unjustified" but its decision comes after two international hospitals and their researchers contacted them "as late as the last 24 hours" to say they have "fresh evidence about their proposed experimental treatment".
Under a High Court ruling, GOSH is forbidden from allowing Charlie to be transferred for nucleoside therapy anywhere. GOSH also points out that the ruling calls for Charlie's artificial ventilation to be withdrawn and he should receive palliative care only.
Yates has said her son was "not in pain or suffering" and she had been given hope by international attempts to come to Charlie's aid, including from the Pope and President Donald Trump.
GOSH said it will now be for the High Court to make its judgment on the facts and it is acting in Charlie's best interests. They describe his condition as exceptionally rare, with catastrophic and irreversible brain damage. GOSH said on Friday their view the treatment would be "futile" and could prolong the boy's suffering had not changed.
Previous legal attempts by Charlie's parents failed as judges in the High Court, Court of Appeal and Supreme Court in London ruled in favour of GOSH doctors, while the European Court of Human Rights declined to hear the couple's appeal.
Charlie's case will be heard by Mr Justice Francis on Monday at 2pm, according to a High Court listing.
