Barnardo's, the Children's Society, NCB (formerly National Children's Bureau), NCH, NSPCC and Save the Children were invited to send staff and service users, including young people and parents, to discuss future policy on children's services.
"This is a genuine attempt to engage with you and make things better," Children's Minister Margaret Hodge told delegates at the event last Thursday.
"Some of the ideas that you come up with will help form our manifesto as we move towards the next election. As we all know, a little idea can grow into a programme and go on to change people's lives."
The charities discussed six themes including tackling child poverty, child protection policy and involving young people in decision making.
They presented their findings to Tony Blair and Margaret Hodge.
The organisations emphasised the sector's need for more sustained funding of programmes over many years.
"It is clear that we need to use more local and voluntary groups to allow more local creativity and flexibility," said Blair after listening to feedback from delegates. "Having listened to your views, we will come back with some ideas based on what you have said."
But some delegates were unsure about how much impact their opinions would have.
"It was a good exercise for those who haven't been involved with policy before, but much of what we discussed has already appeared in the Every Child Matters Green Paper," said Laura Brownlees, policy officer at Save the Children.
NSPCC children's services manager Timur Djavit said: "Many of us came along with a certain amount of scepticism, but overall it has been positive."
After the event, coined 'the big conversation on children', Blair hosted a reception at Number 10 to thank those who were involved in developing the Green Paper, which was instigated following the death of Victoria Climbie.