The incident took place when they were returning from Shukratal after taking an auspicious festive bath on the occasion of Buddha Poornima yesterday, they said.
The deceased were identified as Gyandas (60), Ashika (1) and Yash (9).
The injured were rushed to hospital in serious condition, police said.
The truck driver fled with his truck after the incident, they said, adding, a case has been registered and investigations are underway.