Bidhya Sagar Das, an Indian-origin man living in Finsbury Park in London, was on Tuesday charged with the murder of a one-year-old boy and critically injuring the toddler's twin sister, believed to be his children.
Scotland Yard had arrested Das, 33, on Sunday after they were alerted to the incident. The boy, Gabriel, died in the early hours of Sunday and the girl, Maria, is in critical condition in hospital.
A post-mortem examination is due to take place and Das will appear in court on Thursday. Forensics officers were also seen photographing an orange and black claw hammer found near the crime scene.
The Metropolitan Police in a statement said detectives from the Homicide and Major Crime Command, led by detective chief inspector Dave Whellams, continue to investigate.
"This is clearly a tragic incident, and our thoughts are with the family of the two young children," Whellams said.
The twins lived on the top floor of the building on Wilberforce Road near Finsbury Park with their Romanian mother, Cristinela Datcu, and Indian-origin father.
Horrified neighbours had reported a woman, believed to be the children's mother, rushing out of the home screaming, "My kids, my kids!" shortly after 11pm GMT on Saturday.
Das reportedly worked as a night receptionist in a neighbourhood hotel.