More demonstrators have gathered in an "exclusion zone" to test the limits of a law banning protests without the police authorisation.
No-one was arrested during the protest
Catholic peace group Pax Christi read out names of children killed in the Iraq conflict at Downing Street.
Members said prayers at the event, which did not have police permission, but officers chose not to intervene.
Maya Evans, who read out names at the Cenotaph of soldiers killed in Iraq, has been convicted under the new law.
The 25-year-old was found guilty of breaching Section 132 of the Serious Organised Crime and Police Act, which covers a half-mile area around Parliament, and given a conditional discharge.
Since her conviction, others have been testing the new law - originally designed to evict peace protester Brian Haw, whose anti-war vigil has been a fixture in Parliament Square for four years.
He remains in the square, having successfully fought his case in the High Court.
On 21 December, about 100 carol singers gathered in Parliament Square, but no-one was arrested.
Pax Christi's British chairman Stuart Hemsley told the BBC News website he read out the names of 29 British soldiers with children, who had been killed in Iraq.
The group also picked out the names of 50 Iraqi children aged five and under.
"We had no problems from the police whatsoever, they just stood there looking stony-faced. It was as if we weren't there.
"I am not disappointed I have not been arrested but I wonder if this will now set a precedent."
He said the group of 15 wanted to pray and worship at the seat of power in the hope they would continue to raise awareness of the situation in Iraq.