A 27-year-old woman on Sunday poisoned her two children aged five and two in Nyahururu.
Grace Wambui reportedly administered pesticide to her sons at around 9 am.
The younger minor succumbed to the pesticide on Monday while undergoing treatment at the Aljabet hospital.
Confirming the incident, Nyandarua North police boss Timon Odingo said they are yet to establish the motive of the shocking incident.
The boys had been living with their grandmother, Jane Nduta, after Wambui sent them away three months ago.
On Sunday, their grandmother had gone out to find food to cook for the children when the mother poisoned them.
According to a family member, “Wambui locked herself with the children in the house.”
“Moments later, I heard them sneezing. The children were found frothing in the mouths.”
Police rushed the boys to the hospital in critical condition and arrested their mother.
She was initially charged with attempted murder at a court in Nyahururu.
“Following the demise of one of the children, we are contemplating charging the woman with murder,” said Mr Odingo.