Children in England are left in care for nearly 21 months on average before being adopted, according to new figures.
In some areas, youngsters are forced to wait almost three years before moving in with an adoptive family.
Ministers said it was unacceptable that some children were waiting several hundred days to be adopted.
More councils in England are now failing to meet the Government’s threshold on how long a child should wait between being taken into care and moving in with their new adoptive parents, the statistics show.
The latest adoption scorecards published by the Department for Education (DfE) shows the performance of each local authority in finding children new adoptive homes.
Children now face a 636-day wait on average, equivalent to almost 21 months, between entering care and moving in with an adoptive family. But there are wide variations across the country.
Kensington and Chelsea in west London has the longest waiting times, with children in care for an average 1,082 days, equivalent to 35.5 months or almost three years, before moving in with an adoptive family. Wolverhampton has the second longest time at 936 days, followed by Lambeth in south London at 933 days.
Children in care in West Berkshire have the shortest wait at 405 days, equivalent to 13.3 months.
The Government has set a threshold of 21 months (639 days) between children being taken into care and moving in with an adoptive family.
For the councils which have figures available, 63 are not meeting the threshold, compared with 59 who were not when the first adoption scorecards were published in May.
The scorecards also show how long children in care have to wait between a council receiving court approval to find them an adoptive home and finding a match with a family.
Ministers have set a threshold of seven months (213 days) for this.
Across the country, children in care are waiting 195 days on average between an order being made and a match being found.
Among the councils which have figures available, 48 are not meeting this threshold.
In total, 37 councils in England failed to meet both of the thresholds, the DfE said.
Children’s minister Edward Timpson said: “Children awaiting adoption deserve to be placed with loving families more quickly. Instability can cause real damage to a child’s chances.
“It’s crucial that we make sure that paperwork and processes do not lead to unnecessary delays.
“It is not acceptable that children wait several hundred days longer to be placed with adoptive families in some areas of the country.”