The tragedy occurred in the northern Philippines, police said.
The nine other occupants of the small bus were injured, as were 17 travelling on the bigger bus, according to an updated tally released by regional police.
“They (the family) were trying to catch a mass in Manaoag,” Agoo police officer Vanessa Abubo told AFP, referring to a northern Philippine town near Agoo with a famous Catholic church.
The centuries-old Our Lady of Manaoag church is a popular pilgrimage site in the mainly Catholic nation, featuring an icon of the Virgin Mary which the faithful say performs miracles.
Agoo police chief Roy Villanueva told Manila radio station DZMM by telephone that the smaller vehicle had left its lane to overtake a third vehicle.
Authorities are investigating whether the driver, who Abubo said was among those killed, had fallen asleep or was under the influence, Villanueva added.