Members of the public broke into the house through a window to save the family, but the man confronted them with his machete.
Unbowed, they regrouped, chased the man and beat him to death.
The child died while undergoing treatment at Kisau Health Centre.
The woman was rushed to Makueni Level 4 Hospital.
The bodies of the man and his son were taken to Makueni Level 4 Hospital mortuary.