The United Nations children's fund Unicef says children should have a say when they are adopted and when their parents separate.
The agency's New Zealand branch says adoption and family laws breach the UN Convention on the Rights of the Child, which New Zealand ratified 20 years ago this year.
Advocacy manager Deborah Morris-Travers, who adopted a baby herself eight years ago, said it was impractical to consult babies about being adopted, but it should be compulsory to consult older children.
"With the numbers of children in foster care and the efforts to create 'permanency' and 'home for life', there are a number of children who will find themselves in a situation of potential adoption."
She said adopted children should also have a legal right to find information about their biological parents. Current law allows this only from age 20. "They should be able to access information at the time they start asking questions."