At least six children were killed on Sunday when shells fired by Syrian government forces slammed into a kindergarten school building in a rebel-held suburb near the capital Damascus, authorities said.According to the Syrian Observatory for Human Rights, the shells slammed into the kindergarten while the children were reportedly playing in the school yard in the rebel-held suburb of Harasta, Xinhua news agency reported.Harasta, one of the key rebel-held areas near Damascus, is adjacent to the international road connecting Damascus with central and northern Syria.The rebels in Harasta have repeatedly fired sniper shots at passenger buses on the international highway, prompting the government to assign a sub-road for passengers to avoid passing the area.