The slaughter - the worst atrocity of the nation's brutal civil war - came just days after a United Nations weapons inspection team arrived in Syria.
According to the Mirror, responsibility for the sarin-style nerve gas bombardment in the Al Ghouta area, east of the capital Damascus, was immediately denied by President Bashar al Assad's regime.
Officials dismissed the claims as illogical and fabricated, saying that it was a sign of 'hysteria and floundering' by the government's enemies.
Foreign Secretary William Hague vowed that those behind the brutal attacks would be held to account.
He added that if verified, this would mark a shocking escalation in the use of chemical weapons in Syria.
Hague's concern was echoed by the European Union, which stressed there was a need for a 'thorough and immediate' investigation.
The Turkish Foreign Ministry branded the killings a crime against humanity.
According to the report, unverified images showed lines of dead children, their bodies wrapped in shrouds ready for burial.
The death toll is said to be the highest for a single day in the two and a half years of civil war that has claimed more than 100,000 lives on all sides.