The criticism came during the second reading of the Children and Social Work Bill in the House of Lords.
The legislation, announced in the Queen's Speech last month, includes plans to require councils to ensure care leavers are aware of support on offer, introduce a new system of regulating social workers, allow councils to be exempt from some social care legislation, improve the adoption process and introduce a centralised system for reviewing serious safeguarding incidents.
But Labour's Lord Watson criticised it for being a "skeleton bill" that offers little substance about how these new procedures and systems would be introduced, saying that these necessary details seem to disappear "off into the mist".
He added that it was so lacking in detail that the bill in its current form is "treating Parliament with contempt".
Former children's services commissioner in Birmingham, Lord Warner, was particularly critical of the "rag-tag" bill's plans to overhaul social work regulation.
He branded these plans "ill-thought-through changes", adding that following years of upheaval in children's social work "it beggars belief" that ministers "now want to take wide powers to throw all of the social work regulatory cards up in the air again".
Independent peer Lord Bichard was critical of plans to improve support for care leavers, saying that in their current form they place too much responsibility on young people to request support. "Let's place the onus on the authority, not the care leaver," he said.
Bichard, who headed the 2004 inquiry into the murders of two Soham schoolgirls in 2002, also criticised the bill's plans to overhaul serious case reviews (SCR).
He said the problem with the current SCR system was a "failure to translate lessons into action" rather than the reviews themselves.
Education minister Lord Nash defended the bill, saying that it "represents an opportunity to dramatically improve the way this support is offered after years of these children being often left behind".
Children's rights group Article 39 has also criticised the bill, saying it will remove children's rights and safeguards. This includes the bill's plans to relax the assessment process on placements with family and friends and removing independent reviewing officer (IRO) support for children in care considered to be "low risk".
In its response to the bill's second reading, Article 39 said: "Without detailed plans from the government, it is impossible to identify which looked-after children ministers or local authorities might consider to be low risk."
It is also concerned that once an IRO is removed, a child may not be able to access them again while in care.