Kindergarten head Shi Haixia poisoned the children last year in a revenge attack aimed at a rival school in Hebei province which had higher enrollment, state broadcaster CCTV reported.
A court in Hebei sentenced Shi and an accomplice to death, while another person was given a five-year jail sentence, the report said.
Two village girls died after their grandmother found the yoghurt, which was laced with rat poison and placed on a roadside along with several notebooks, state media reported earlier.
China has a shortage of state-run kindergartens, and competition between private profit-driven institutions can be intense.
Many children in China's countryside are cared for by their grandparents because their parents have migrated to cities to find work.