Carol Homden, chief executive of children's charity Coram, said she is concerned that the plight of youngsters waiting to find a new family has fallen off the political agenda amid the "turbulence and uncertainty" of the last year.
She urged potential adopters to come forward, saying that adopting a child is one of the greatest, but most rewarding challenges a parent can face.
Figures published by the Department for Education earlier this month showed that the number of children being adopted has fallen for the fourth year in a row.
Overall, 3,570 children were adopted in the year ending on March 31, down 7 per cent on the previous year, and down a third (33 per cent) from a peak of 5,360 in 2015.
Dr Homden said: "I am concerned that the plight of this vulnerable group of children has slipped off the agenda amid the political turbulence and uncertainty of the last year."
She said that her charity was seeing a high number of people who inquire and express an interesting in adoption, but a reduction in the numbers who progress their application.
Dr Homden also told PA: "It's extremely important that the message continues to be conveyed that our most vulnerable children need adopters to come forward, and that that is a priority for society that they do so."
She went on to say that adoption is not the right path for every child, and one form of placement must not be put above another, adding that it is "society's job to do its best by all of its children and we need people to come forwards who are willing to care for them, in whichever type of approach suits their needs".
Dr Homden acknowledged that successive governments have recognised the importance of supporting children in the care system, and enabling them to leave the system into a "long-term permanent loving home".
"What I'm calling for is that people all across the sector and of all political persuasions remember there are too many children waiting for adoption and we do need to encourage and enable all who could care to come forward."
Dr Homden also urged members of the public "to spend some quiet time considering whether they could offer a loving and permanent home to a child in need".
"Adopting a child is one of the greatest challenges that a parent will face but it is also one of the most rewarding," she said.
Official figures show that as of the end of March, for children in England, the average time between entry into care and adoption was one year and 11 months, with older children waiting slightly longer than younger children.
A local authority will take the decision on whether a child should be placed for adoption, and then a formal placement order is made.
Statistics show that as of the end of March, there were 2,750 children with a placement order who had not been placed for adoption.
This figure does not include children for whom the decision has been taken that they should be adopted, but no order made.
In the year to the end of March 2019 alone, decisions were taken that 4,170 children should be adopted.
Separate figures from the Adoption and Special Guardianship Leadership Board indicate that there were about 3,000 families approved for adoption in 2018/19.
A Department for Education spokesman said: "Every child deserves to have a loving, stable home that's right for them - that is why adoption is a top priority for the new Government.
"The Education Secretary recently announced a £46 million package of support to prioritise adoption, helping to recruit new adoptive parents and support new families as they adjust to their lives together."