The union says some children are not being allocated court guardians
The body protecting children in family courts is going through unprecedented strain, a union has warned.
The Children and Family Court Advisory Support Service (Cafcass) has seen a record rise in child care applications in England since the Baby Peter case.
Union Napo said children were suffering because Cafcass was too stretched to allocate them all a guardian to represent their interests in court.
Cafcass said it offered children a safe service despite facing challenges.
Napo, which represents probation officers and other family court staff, said Cafcass was suffering issues with its workload, resources and morale.
The union said hundreds of children were still waiting for Cafcass to appoint a guardian to them because caseloads had virtually doubled for some frontline staff.
Budgetary problems meant the number of guardians was actually being cut in some areas despite the increased workload, it added.
The union said the situation was so critical staff were considering taking industrial action.
The union's findings were contained in a briefing paper prepared for MPs and seen by the BBC.
'Emotionally and psychologically'
Napo assistant general secretary Harry Fletcher said children were getting a deteriorating service.
He told the BBC: "I think it's inevitable that children must suffer if staff have 20 cases or more instead of 12 which they had a year or so ago.
"If care cases aren't being allocated because there are insufficient guardians, therefore nobody is representing the child in legal proceedings, then clearly children must be suffering, both emotionally and psychologically."
Seventeen-month-old Peter Connolly - known as Baby P until the court case over his death ended - died at the hands of his mother, her boyfriend and their lodger in August 2007.
Cafcass has also been criticised in the annual report of watchdog Ofsted.
It said four out of five Cafcass regions inspected last last year were inadequate, and the pace of improvement at the organisation was too slow.
A Cafcass spokesman said that while it faced a number of challenges it continued to offer children a safe service.