The Syrian Observatory for Human Rights yesterday said the attack targeted a checkpoint in a town controlled manned by Kurdish forces in the Qitna area.
Four Kurdish fighters at the checkpoint were killed, as were two children, it said. More children were among 10 people wounded.
Kurdish fighters in the area are battling jihadist fighters from the Islamic State group.
The war in Syria began in March 2011 with peaceful protests against President Bashar al-Assad's government, but quickly escalated into an armed rebellion after a brutal regime crackdown.