The incident occurred yesterday when the victims along with two others were proceeding to Namakkal district, they said.
When the motorcycle approached Lakshminagar, a lorry coming in the opposite direction dashed against the motorcycle.
In the impact, all the four were tossed in the air, they added.
While Jayalakshmi and Ritish(18 months) came under the front wheel of the lorry and were killed on the spot, Somasundaram, who was riding the bike and the two-month-old baby girl sustained serious injuries.
A case has been registered and a search is on for the lorry driver.
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