The Fostering Network, Voice, and The Adolescent and Children's Trust (Tact) are preparing to lobby MPs to include the change in the Children and Young Persons Bill, which is about to be debated in the House of Commons.
The charities want children to be able to stay in foster care up to the age of 21 and not be forced to leave before they are ready. Tact is sending postcards to MPs asking them about the age they left home to get them thinking about the issue.
Adam Hug, the Fostering Network's policy and campaigns manager, said: "What the government has come up with since the Care Matters paper is a number of pilots. We want to see a commitment from the government to roll out these pilots across England."
John Kemmis, chief executive of Voice, said there would also be a push for better advocacy services for children in care. The British Association for Adoption & Fostering is to call for better access to information for adults who have left care.
Kevin Williams, Tact's chief executive, said the charity would lobby for a virtual health expert, with a role similar to a virtual headteacher, who would oversee the education of all looked-after children in their area.
