Jamie Leek of Clifton, Nottingham died in Zante in June 2012 when he was hit by motorcyclist Spiridon Koklas.
A Greek appeal court has upheld his sentence of four years and 10 months but suspended it for three years.
Jamie's mother Lydia said the family "feel cheated of justice".
"We are mortified by this and at a loss for words. We have to accept it is probably the end of the line in legal terms," she said.
Jamie and his family were on holiday in the resort of Kalamaki to celebrate his parent's 10th anniversary when he was hit crossing the road with his father.
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The day he died was his ninth birthday.
Mr Leek suffered a broken arm in the accident but Jamie died later in hospital.
Koklas was convicted of involuntary homicide and involuntary bodily harm in 2015, but had appealed his sentence. He was not in court for the appeal hearing.
After a previous hearing, Mrs Leek said the rider "didn't show any remorse to us at all. He didn't show he was sorry one bit".
The family have been supported by Nottingham South MP Lilian Greenwood, who has asked two prime ministers  - David Cameron and Theresa May to help raise the issue.
Both promised the MP they would help the family by contacting the Greek authorities.
Ms Greenwood said: "I am really shocked, angry and upset that despite the long quest for justice for their son Jamie it has resulted in what feels like a totally inadequate sentence.
"It has taken several years to get to this stage and then for the sentence to be suspended feels like a complete kick in the teeth."

Transport Minister John Hayes said he was satisfied the local council would be financially protected in a proposed Compulsory Purchase Order.
And he has paved the way for a search and rescue helicopter service to return to the airport - which closed last year - "when" it opens.
But the airport's new owners, Trevor Cartner and Chris Musgrave, claim his statements breached election rules.
After 30 March, the general election pending period prevents the government from making announcements about new or controversial matters.
Mr Cartner and Mr Musgrave said the timing of his statement was "a disgrace" and Mr Hayes as Transport Minister "should have exercised an element of impartiality and objectivity".
"We are now taking legal advice with a view to making a formal complaint to the Electoral Commission," they added.
Mr Hayes described his announcements as "huge steps towards securing Manston's future as a working airport".
Dr Beau Webber, of the Save Manston Airport Campaign, said: "This means Manston has a chance... we have good people who want to put good jobs in place for Thanet."
The airport closed in May 2014, seven months after being bought by Stagecoach Group co-founder Ann Gloag.
A majority stake was sold to Mr Cartner and Mr Musgrave for redevelopment several months later but the nature of the sale and the true ownership of the airport was called into question by a recent Commons Transport Select Committee.
Financial risk
The government has supported a "five point plan" to reopen the airport, including compulsory purchase of the site.
However, there has been concern about the financial indemnities offered by RiverOak - the US firm interested in buying and running the airport.
But Mr Hayes said on Thursday that he was "satisfied by the indemnity offered by RiverOak to protect the council against the costs of the Compulsory Purchase Order".
RiverOak's Stephen DeNardo welcomed the news and said it remained "absolutely committed to reviving Manston as an operational airport".
Bristow, the company that provides search-and-rescue services for the Maritime and Coastguard Agency, had originally planned to base two helicopters at Manston.
The government has now announced that instead of agreeing a long-term contract for Bristow to base its helicopters elsewhere, it has agreed a one-year deal to temporarily base them at Lydd Airport, also in Kent.
Labour, the Liberal Democrats and UKIP also support the reopening of Manston Airport but have criticised the way the Conservatives have handled the issue.
The family of a nine-year-old British boy who died after being hit by a motorcyclist in Greece five years ago are "mortified" that the driver will not be jailed.
[NEXT_CONCEPT]
The fight to reopen Kent's Manston Airport has received a double boost.