What was the first children's educational program to debut on public television?

This is a difficult question to answer, since there were a few locally-produced children's programs on some public television stations in the mid-1960s, back when it was still called NET (National Educational Television). One of the first children's programs to become popular nationally was "Mister Rogers' Neighborhood," which debuted on NET in February 1968 (after first being on the air in Canada). Another famous early children's program was "Sesame Street," which debuted on NET in November 1969. Both programs continued on when NET became known as the Public Broadcasting System (PBS) in late 1970.