On Tuesday Brett King, 51, and his wife Naghemeh, 45, were released from Spanish custody after a European arrest warrant was withdrawn.
The couple were detained after taking five-year-old Ashya, who has a brain tumour, from a Southampton hospital last Thursday against medical advice.
The family say they went to Spain to sell a family home to pay for proton beam therapy, which is available in the Czech Republic.
Ashya's brain tumour was successfully removed last month, but it is thought the therapy would help prevent its return.
The story sparked a public outcry for the parents to be released to allow them to be at their son's side in the Spanish hospital.
Numerous politicians called for their release including Northern Ireland's deputy First Minister.
And an online petition calling for the child to be reunited with his parents attracted over 200,000 signatures.
Ethan Dallas, 16, a friend of Ashya's brother Naveed, who started the petition, delivered it to Downing Street and said the case had "touched the heart of nations".
The case has struck a chord with Stephen and Leona Knox and their own experience of trying to save their son.
They took to social media to highlight their son's plight two years ago after he was diagnosed with an aggressive form of cancer.
Wee Oscar died aged five in May, after a brave battle against neuroblastoma.
Speaking to the Belfast Telegraph, Leona has spoken about the loss of her son which she said was "every bit the nightmare you think it's going to be".
"I didn't think I could cope with my child having cancer, I didn't think I could cope with him dying - but you don't have a choice," she told the paper.
Leona spoke of the impact it has had on their four-year-old daughter Izzie, who she says is "lonely" since Oscar's death.
In October 2012, after raising £250k through their campaign, Leona and Stephen took Oscar to America for specialist treatment not available in the UK, unfortunately on arrival at the hospital in Philadelphia, he was found to be unsuitable due to an issue with his heart.
On Twitter, his mum compared the two cases and asked: "What if we had been taken away from him for seeking the best treatment abroad and charged with neglect? I just cannot believe the injustice.
She added: "What if we had been threatened with court when we realised Oscar needed treatment unavailable on NHS? What if his consultant didn't back us?"
Oscar's dad Stephen described the Kings' arrest on Twitter as "wrong". He shared the online petition for their release and encouraged others to sign it.
UK deputy Prime Minister Nick Clegg has also expressed concern for the little boy and his family.
"I understand people's widespread reaction which is you can debate or not whether that is the right treatment or not for this little boy, but for heaven's sake, keep this little boy and his family together," he said.
"Throwing the full force of the law at two parents who, in some state of despair and anguish, are acting, they say, because that's what they think is best for their own child, doesn't seem to me to be the appropriate thing to do."
Prime Minister David Cameron also called for Ashya to be reunited with his family and said seeing pictures of the five-year-old boy brought back memories of his son Ivan, who he lost to an illness in 2009.