The Scottish Kinship Care Alliance staged a loud and colourful demonstration at the Scottish Parliament and told ministers that the Children and Young People Act discriminates against children looked after by family members.
The group met children's minister Aileen Campbell to tell her the act increases the gap in how children of kinship carers are treated compared with children in foster care.
Children in foster care receive greater financial support than those in kinship care and can access a greater level of services.
The group argues children in kinship care but with looked-after status who will move to a new status under kinship care order will get less support.
It claims leaving decisions about support such as educational assistance and psycholo-gical support will lead to a "postcode lottery" with different criteria in different areas.
Scottish Kinship Care Alliance chairwoman Anne Swartz said: "The Scottish Government claim they are 'getting it right for every child' but kinship children remain stigmatised and discriminated against.
"This is a wake up call to the SNP to stop trying to limit support in the Children and Young People Act, put serious finances behind kinship care, and make Scotland truly the best place for vulnerable children to grow up."
The group wants a minimum level of financial support for kinship carers to cover the basic costs of caring for a child and says a government review was due last year but has not been published.
Kinship carer Tina Hendry said: "Children in foster and kinship care have the same stories, the same needs, and can even be brothers and sisters, yet they are treated totally differently by local authorities and the Scottish Government.
"Kinship carers are not asking for a wage, or any great reward, just the most basic services and support to help the children in their care cope with the trauma, separation and poverty they experience.
"Surely this is not too much to ask."