Angry parents say they want the graves to serve as a reminder that the children died due to state negligence.
A doctor at the local hospital said a chemical used in pesticides was the likely cause of contamination.
In all, 47 primary school children fell ill after consuming the meal of rice and soybeans on Tuesday.
Twenty-two were confirmed dead on Wednesday. A day later Bihar's Principal Secretary Amarjeet Singh confirmed another of the children had died.
Officials say the headmistress of the government school, in the village of Dharmasati Gandaman in Saran district, has fled.
Some children at other schools in the state are now reported to be refusing to eat the free meal.
"We have received complaints that children in some schools in four or five districts have refused to eat the midday meal. We are trying to resolve the issue," Laxamanan, the director of the Mid-Day Meal scheme in Bihar, told the BBC.
The scheme provides free food for students, but often suffers poor hygiene.
It was introduced to combat hunger and boost school attendance, and reaches 120 million children in 1.2 million schools across the country, according to the government.
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