The attack took place at 10 am in the village of Oe Htein Kwin, about ten miles northwest of the epicenter of the earthquake on March 28.
We tried to scatter the children, but the warplane was too fast and dropped the bombs, says a teacher who wants to remain anonymous.
In addition to the 20 schoolchildren, two teachers died, adds the witness.
The military junta ruling the country says in a statement that the reports of the attack are "fabricated news" and that no air attack on "non-military targets" has occurred.
The military has previously promised a ceasefire while the work on rebuilding after the major earthquake is ongoing.
