Blair says Leo's healthcare is a private matter
Pressed on the issue by Conservative MP Julie Kirkbride, who has recently given birth, Mr Blair voiced his support for the combined vaccine for measles, mumps and rubella.
Mr Blair's comments came as health issues, including complaints that waiting list figures have been fiddled in some hospitals, once again dominated prime minister's questions.
Keeping private
Ms Kirkbride, who was heckled loudly by Labour MPs, said she understood why Mr Blair wanted to keep details of his children's healthcare private.
But with the government mounting a campaign for children to receive the MMR vaccine, there was a legitimate public interest in the issue.
"The public want to know whether the prime minister practices what he preaches," continued the MP.
The prime minister told the Commons: "I'm not going to enter into any public discussion on the health of my children."
Mr Blair stressed that the government's recommendation that children receive the MMR vaccine was supported by the World Health Organisation, the British Medical Association and other health bodies.
He continued: "We fully support the campaign that is being mounted at the present time."
The Blairs have come under pressure from some newspapers in recent days to reveal whether Leo did have the disputed jab.
The latest Medical Research Council findings have concluded that fears that autism was linked to the MMR vaccine were misplaced.
Fiddled figures
In his health offensive, Conservative leader Iain Duncan Smith argued it was Mr Blair's "culture of deceit" which had forced health service workers to manipulate waiting list figures.
The Tory leader's attack follows a National Audit Office report showing waiting list figures had been fiddled in nine hospitals in the drive to meet government targets.
Liberal Democrat leader Charles Kennedy also joined the fray over the controversy.
Mr Kennedy argued it was an "absolute scandal" that some of the managers involved had received "golden handshakes" on leaving the service amd some had been re-employed by the NHS.
The problems involved 6,000 operations out of about 25 million performed in the last five years.
Waiting lists overall had fallen by 100,000 since 1997, said Mr Blair, who admitted there was still a "great deal still to do" in improving the NHS.
That picture was unaffected by the new report, continued Mr Blair, but Mr Duncan Smith said the findings meant nobody would believe his claims.
'No escape route'
"The prime minister was elected in 1997 to cut the waiting lists and save the NHS," said Mr Duncan Smith.
"He cannot weasel out of that by saying some of it's good and some of it is not."
Mr Blair countered the accusations by pointing to the extra investment pledged for the NHS.
He seized on comments made by Mr Duncan Smith last weekend, when he refused to rule charging to see GPs as a way of raising money for healthcare.
Mr Duncan Smith told the BBC people already paid for some services, such as dentists, as well as for prescriptions.
But Mr Blair insisted Labour was instead committed to keeping the health service free at the point of delivery rather than "Tory charges".