The United Nations Convention on the Rights of the Child in 1989 was the first 
international acknowledgment of the position of children in society and their right to protection, participation and provision of resources. This does not directly address child poverty but living in poverty will detrimentally effect the ability of a child to achieve these rights. The Convention did not outline the way in which states should work to ensure these rights for children and as a result it did not lead to significant policy responses.
A complete copy of the convention can be found here.