The deputy headteacher was leading her pupils from St Jude and St Paul's C of E primary school, Islington, on a trip to the Houses of Parliament when terrorists launched their rush-hour bomb attacks on the capital.
"My headteacher called, she wanted me to turn round and come back to school but I am afraid I carried on regardless. I thought the House of Commons would be the safest building in Britain for the children," she said.
The call was Ms Ashwin's first warning of the chaos which was to grip central London last Thursday after four bombs were planted on tube trains and a bus. But, locked in the corridors of power for seven hours, with armed police on guard outside, the St Paul's children seemed oblivious.
"The children were very excited to see all the police with guns when they got to the Houses of Parliament. The children saw it as a bit of a holiday.
They thought they were going to have to stay there all night," said Ms Ashwin, who was finally able to take the pupils home by bus at 5.30pm.
Across the capital, thousands of pupils were told to stay at school.
Westminster, Camden and Tower Hamlets councils telephoned and emailed heads around 10.30am to tell them to keep pupils indoors until parents collected them.
At Sir John Cass's foundation primary, near Aldgate tube station, scene of one of the blasts, all 270 pupils were rushed into the basement before being evacuated.
Many youngsters, some as young as three months old, were taken to the nearby Shapla primary school, which was designated as an evacuation site 10 years ago following IRA bombs in London. Its hall windows are reinforced to protect them against explosions.
Jane Wallace, head of Shapla school, where all but one of the 220 pupils are Muslim, said: "We have had a few comments from the children asking if Muslims did this. I said maybe but mainly we have good Muslims and these people are sick."
In Tower Hamlets, three schools were turned into emergency centres, with gyms acting as temporary shelters for people displaced by the bombings.
Doctors, nurses, psychologists and social workers were drafted in to each school and one, Bishop Challoner, was also used as a police witness interview centre.
Most schools in Westminster stayed shut last Friday as investigations into the bombings, which claimed more than 50 lives, continued. Heads in the borough will have access to counselling services. Prayers were said during assembly at Gateway primary, the only school in Westminster to open on Friday. The school is just a few minutes' walk from Edgware Road station where at least seven people were killed.
Keith Duggan, the headteacher, said: "We emphasised the fact that it is ordinary people who suffered like them, their mums and dads."
Officials from the Department for Education and Skills, warned that some pupils might need counselling to help them overcome trauma. Kevan Collins, the Government's national director of the primary strategy, said: "We need to talk about what has happened with children, and children should have the opportunity to share their views."
A factsheet to help teachers and pupils cope with the bombs is at www.teachersupport.info Teachers can also call the Teacher Support Network on 08000 562 561 and pupils can ring ChildLine on 0800 1111. A kit to support assemblies about the blasts is at www.redcross.org.uklbak