The BBC's Sarah Rainsford in Tarragona, Spain, said the judge would decide on Thursday whether to press formal charges. The three entered the court with their coats pulled over their heads, she added.
Sahil was seized during a robbery at his grandmother's home in the Pakistani region of Punjab in the early hours of 4 March, then freed 12 days later.
The case has so far spanned four nations and has seen an array of twists and turns, involving a family spread across two continents, investigators in Pakistan, the UK, Spain and France, and international police organisation Interpol.
Following an emotional reunion with his son at the home of the British High Commissioner in Islamabad, Raja Naqqash Saeed thanked everyone for their messages of support over the last fortnight.
"I am completely overjoyed that I have been reunited with my son after such a long ordeal.
"Sahil is doing well, is in good spirits, and can't wait to return to the UK to see his mum, his family, and join his friends back at school."
AT THE SCENE
Shelley Thakral, BBC News, Islamabad
Today, on the lawns of the British High Commission in Islamabad, a fabulous scene was played out.
For two weeks the media had been showing a family video of football-mad Sahil playing at home in the UK.
Now, the little boy was running around again. This time, in the Islamabad sunshine, with his father Raja Naqqash and two-year-old cousin Saher.
Watched over by his grandmother, aunt and uncle, Sahil posed happily for the cameras, and at one point stopped to put his foot on the football and hands on hips. His proud father, Raja, called it his "Beckham pose".
Just hours after Sahil was kidnapped his father told us Sahil was his best friend: ''We do everything together,'' he said.
Today they were inseparable. Father and son shared hugs and kisses - ''one more, one more,'' Raja kept asking.
Sahil's mother Akila has been back at the family home in Oldham throughout her son's ordeal. They are expected to be reunited on Thursday night back in the UK.
In the arms of his dad his message to her was ''Mummy I love you, mummy I miss you''.
He also paid tributes to the "tireless efforts" of the Pakistani and UK authorities that ended with the "safe return of Sahil to us".
Mr Saeed asked that on their return to the UK the media "shows restraint and respects our family's privacy as we spend some quality time with Sahil".
Speaking after the reunion British High Commissioner in Pakistan, Adam Thomson, said Sahil had met his father along with other relatives who had brought the boy to Islamabad.
"I can imagine it's a very emotional moment for them all," he said.
The first pictures of Sahil showed the five-year-old, with a shaven head, playing football in the sunshine with his father and a little cousin.
While Sahil was in captivity a phone call made from Spain had instructed the boy's father to travel to Manchester and then Paris, where police watched him hand over the cash in a public street.
Earlier, Pakistan's interior minister said some money had been paid within Pakistan to get the child freed.
Spanish authorities were alerted by Interpol after the call was traced to Spain, and police there said the initial phone call gave the family three days to pay the ransom.
Unconfirmed reports in the Manchester Evening News have suggested Greater Manchester Police helped "facilitate" the ransom payment, but the force refused to confirm or deny the claim.
Spanish officers said police in Paris watched as people took the money handed over by Sahil's 28-year-old father and divided it into a bag and trolley.
French police then followed them to the border with Spain.
As soon as they were confident Sahil was safe armed Spanish police officers in Tarragona, Catalonia, raided a flat in nearby Constanti. They arrested two Pakistani men and a Romanian woman in connection with the kidnapping.
'Ransom suitcase' found in Spain
Some £110,000 in cash, a computer and some mobile phones - used to contact Sahil's father in Pakistan to demand the ransom - were found at the property.
Two of the group had driven to the French capital to collect the ransom payment and were arrested as they returned to Spain. All three are due to appear in court in Spain on Thursday.
Two people have also been arrested in Paris.
Sahil's family were "ecstatic" when he was freed on Tuesday, some 12 days after the kidnap in Jhelum.
Locals had found the little boy wandering in fields near a school about 20km (12 miles) from his grandmother's house.
Speaking on the day he was found his mother Akila Naqqash said she was "gobsmacked" at Sahil's calm reaction when they spoke on the phone.
"He spoke to me like nothing had happened. "He was going on and and on like any other little boy would.
"He said, 'Mummy, are my toys safe? I am going to bring everyone presents, I going to buy them presents for when I come home'."
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