"In 'drug free' Bihar, a BJP leader under the influence of liquor kills nine innocent children. Nitish ji, is this the truth of your prohibition?
"The voice of your inner conscience is saving whom - the accused BJP leader or the truth of liquor in Bihar?" he said on Twitter.
At least nine children were killed and about 20 injured when a speeding Bolero SUV ploughed through them outside a government school on the outskirts of Muzaffarpur town on February 24.
Nitish Kumar had ordered a "speedy probe and tough action against the guilty driver".
The vehicle belonged to a BJP leader from the adjoining Sitamarhi district, police said.