Harriet Harman has urged the Prime Minister to take in a further 3,000 refugee children who are already in Europe.
The acting leader of the Labour party said many were orphans and in urgent need of a home.
She also asked for assurance any children granted asylum would not be deported once they turned 18.
Cameron said Britain would be taking children, including orphans, from Syrian refugee camps, and that they would be allowed to stay once resettled.
But he said experts had warned about the "dangers" of taking children further away from their parents.
Cameron has committed to letting 20,000 migrants into Britain by 2020.
He said a meeting would be held on Friday to determine how many will be taken in by the end of this year.
On a visit to Jordan, David Cameron says that the EU must "follow Britain's lead" and fund more refugee camps around Syria.
The prime minister has insisted the UK will not participate in plans to redistribute 160,000 refugees who have arrived in Europe.
Train traffic with Austria suspended as German authorities seek to reduce the number of asylum seekers arriving in the country.