At least five pupils from Mhamarani Primary School have been admitted to Mpeketoni Sub-County Hospital after eating poisonous fruits.
The learners are said to have plucked the fruits of Jatropha tree in the school compound.
The plant produces oil used to produce bio-fuel.
A foreign company is said to have introduced the plant in Lamu and Tana River counties, as it sought to cultivate it to generate bio-fuel used as an alternative to fossil fuels.
The firm was forced to abandon the project after environmentalists claimed Jatropha was destroying other plants and killing birds that fed on its fruits.
Reports indicated that the foreign firm did not uproot the Jatropha trees that had been planted when the project was stopped.
Residents of affected areas are now asking both the county and national governments to help uproot the plants, which they say are a risk to their lives, and especially those of their children.
At least 69 pupils are reported to have eaten the fruits on Tuesday.
Mr Paul Maina, who is a parent and a teacher at the school, said one pupil who had discovered that the fruits had ripened plucked them and shared with colleagues.
He said one pupil later rushed to the staff room complaining of stomachache and was also vomiting.
On learning that the pupil had eaten Jatropha fruits, teachers visited all classrooms where they found more pupils with similar symptoms.
"All the 69 pupils who had eaten the fruits were taken to hospital. While others were treated and discharged, five are still admitted to the facility as their condition was critical," said Maina.
Those affected are Standard One to Standard Six pupils.
They were first taken to Mhamarani dispensary for first aid before being referred to Mpeketoni sub-county.
Another parent, Ann Muthoni, said her daughter was in stable condition.