About 500,000 children and adults a year are involved in the family justice system
Social workers warn changes being brought in to speed up adoption and the family courts might be bad for the welfare of some children.
Some have criticised a new time-limit for courts to decide whether children should be adopted or placed in care.
A report by the College of Social Work and the Family Rights Group also says changes to the adoption process risk undermining family links.
Ministers want to speed up adoptions in England.
They say children are missing out on finding loving families because of bureaucracy and court delays and are bringing in a new 26-week limit on the time family courts can spend on such hearings.
The government is also proposing tighter controls on the use of experts in such proceedings, including on the standard of their qualifications.
The new report is from the College of Social Work, which has 6,000 members in England, and the Family Rights Group, which advises families whose children are involved with social services.
It criticises a planned change that will mean that once councils have decided to take a baby or child away from their natural parents because they are incapable of looking after them, they have first to consider placing them with a foster carer who might want to adopt them.
The government says this will avoid unnecessary further disruption in the lives of young children caused by moves between foster homes before they are adopted.
But the joint report says the changes could mean “poor decisions” could be made about the lives of individual children “by prioritising adoption over more suitable permanent placements for them, such as being raised by their wider family”.
The groups fear the changes will “squeeze out” relatives who might have been willing to look after a child.
They say such family members often do not come forward straight away, while there is still a chance the child might be able to stay with their natural parents.
The report’s authors say local authorities should instead first have to check whether a child can be placed with relatives before arranging fostering or adoption.
Others have said it can sometimes be better to have a “clean break” from their family.
The government has complained that too many children are stranded in care and that on average, they wait 21 months to be adopted.
The numbers of care orders made on children has been increasing since the death of Peter Connelly, who was known as Baby P.
A spokeswoman for the Department for Education said: “We make no apologies for wanting children to be offered loving homes quickly.
“It currently takes almost two years to place a child for adoption – denying them routine, stability and the opportunity to bond with their parents.
“We know adoption is not right for every child, which is why we are reforming the system so it is better focussed on what each child needs.”
Source: BBC 2013
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