UNITED NATIONS — Twenty years after the U.N. adopted a treaty guaranteeing children’s rights, fewer youngsters are dying and more are going to school — but an estimated 1 billion still lack services essential to their survival and development, UNICEF said Thursday.

The U.N. children’s agency issued a special edition of its annual report on The State of the World’s Children on the eve of Friday’s 20th anniversary of the Convention on the Rights of the Child to spotlight the treaty’s achievements over the past two decades and the challenges ahead.