A man and a toddler have been killed and a woman is fighting for her life after a three-vehicle crash in Sydney's west overnight.Emergency services were called to the intersection of Mamre and Abbotts roads at Kemps Creek at about 10.40pm.They found a small sedan and a van had crashed head-on.READ MORE: Man charged with killing woman, two children in Sydney homeA man and a child have died and a woman is fighting for life after a crash at Kemps