Nearly two-thirds of children in care have been abused or neglected
England's care system needs a radical overhaul with the state acting as a "pushy parent" to get the very best for the children in its charge, MPs say.
A report by the Commons' Children, Schools and Families Committee says the state fails as a "parent" because it does not demand enough from services.
It says concern for the happiness and welfare of the 60,000 children in care should be at the heart of the system.
Ministers say progress has been made, but agree there is more to do.
Of the 60,000 children in care in England, 62% are in that position because of abuse or neglect, others through family illness, "dysfunction", "acute stress" or "socially unacceptable behaviour".
About 4% are looked after because of their own disability, and just under 6% are unaccompanied asylum-seekers.
MPs on the cross-party children's committee say the state fails as a parent because "the government is too timid in demanding that health services and the criminal justice and asylum systems give special consideration to looked-after children".
Children in care or who have left care do not get enough protection from the risks of offending, sexual exploitation or homelessness and there are not enough of the therapeutic services that many of them need, the MPs say in their report.
"We welcome the government's assertion that it should become exceptional for a young person to leave care before they turn 18, and hope that it will precipitate a culture change in local authorities."
They recommend - though without costings - that remaining in care "in some form" until at least age 21 should become routine.
Children in care
60,000 in England
15,000 in Scotland
Twice as likely to be convicted
Seven times more likely to be expelled
Committee chairman Barry Sheerman said: "It is imperative that the government tackles the perception that entering the care system is catastrophic for a child's future prospects.
"It must be seen as a positive experience, but this will only happen if the state can better replicate the warm, secure care of good parents for every child in the system."
The MPs said that, in the case of education, the state was pushing for children in care - by making schools prioritise them in admissions, having designated teachers and mandatory performance indicators.
But it was "too timid" when it came to specifying what looked-after children should be able to expect from health services.
Statistics about the lives of children in care or those who have left care show they do much worse than other children at school.
They are seven times as likely to be expelled and twice as likely to be cautioned or convicted for an offence.
In 2007, 13% of looked-after children in England who sat their GCSEs achieved at least five grades A*-C, compared with 62% of all children.
Samuel says he lacked adult support
While some progress has been made and more children in care are now staying on at school or are working at the age of 19, MPs say, luck plays too much of a role in determining a child's experience "because of inconsistencies in the quality of care".
Establishing close personal relationships between children, families and their social worker and children's services is vital, the report says.
Samuel, who was taken into care at 15 and is now an adult, said he never had a supportive adult to whom he felt he could turn.
"If there had been just one, or even two, steady relationships that I could have had with a social worker or a personal adviser I think that would have helped greatly," he said.
Most looked-after children (71%) are cared for in foster placements.
The MPs said they were concerned about the variations across the country in the rates of children being taken into care, because it seemed "to betray a lack of common understanding about the place of care in services for vulnerable children".
For some children care should be seen as "the best available option rather than a last resort", they said.
Children's Minister Delyth Morgan said a new Social Work Taskforce was being set up to look at the issues.
"We know that outcomes for children in care are not good enough, which is why we put in place record investment and a comprehensive programme to improve outcomes for these children.
"In the last decade we have made progress, with better educational attainment and more care leavers than ever before in employment or training, but we agree there is more to do."