Campaigners for child refugees believe Parliament could change its mind next month and allow unaccompanied children to be resettled in the UK.
The government was defeated for a second time when the House of Lords voted to take in child refugees this week.
The House of Commons originally voted against the amendment to the immigration bill to allow 3,000 unaccompanied refugee children to come to Britain.
The amendment was filed by Lord Alfred Dubs, a Labour peer who fled Nazi Germany in 1939 and arrived in the UK on the Kindertransport.
It was lost by just 10 votes but was passed in the Lords when the commitment to take as many as 3,000 was removed.
"We are optimistic that some of the MPs who abstained last time will now vote in favour," said a spokesperson for Citizens UK, which is leading the campaign for find 5,000 homes in Britain for Syrian refugees.
The House of Commons will vote again on the issue on 9 May.
Juliet Kilpin, Baptist minister and co-ordinator of Urban Expression who has visited the Calais jungle camp several times, has urged people concerned about the child refugees to lobby their MPs.
In a widely-shared Facebook post she wrote: "Wouldn't it be amazing if all Tory MPs who voted not to protect 3000 children stranded in Europe got letters from 3000 children in their constituencies early next week saying how they would feel if they were not welcomed or given refuge if facing danger... and how that might impact their voting habits when they turn18. Might make them reconsider how they vote when the revised Dubs Amendment comes back to MPs. Teachers, head teachers, pupils... ready, steady, go...!!!"
Rabbi Janet Darley of the South London Liberal Synagogue, a different spokesperson for Citizens UK, said: "We are disappointed that the Dubs amendment was rejected in the Commons. It is a national embarrassment that our government is not doing more to help children on our own doorstep. We are failing to live up to the best of our history, exemplified perfectly by Lord Dubs himself who was brought here on the Kindertransport at the eve of the Second World War.
"The number of politicians who voted for the Dubs amendment reflects the strong feeling across the country that we should be doing more to help refugee children who find themselves alone, vulnerable and scared in Europe.
"We also remind the Government that they do already have a legal and a moral obligation to reunite unaccompanied minors in Europe with family members in the UK. The Home Office has only allowed 20 such reunifications while we have 157 eligible children freezing in the mud of Calais ready to go. Citizens UK is calling for the Government to do more to actively identify children and reunite them with family in the UK."
Citizens UK are behind the UK's "Refugee Welcome" movement, coordinating 90 groups across the country. So far in London, just 43 refugees have been resettled, in the boroughs of Camden, Islington, Barnet and Kingston. A further 40 local authorities outside London have offered more than 3,000 places. Other councils are understood to be willing to take refugees if private landlords can be found.
Citizens UK have also helped 20 children from the Calais camp be granted safe passage to the UK to be reunited with family members, including a boy aged 9.
Even the Daily Mail is arguing for hearts not to be hardened over the admission of child refugees. In a comment column the Mail said: "We believe that the plight of these unaccompanied children now in Europe – hundreds of them on our very doorstep in the Channel ports of France – has become so harrowing that we simply cannot turn our backs. It is not their fault, after all, that they've been sent halfway round the world alone to search for a better life, often after seeing family members slaughtered."
