The 35-year-old man, too, has been hospitalised as he slit his throat and wrist.
The case was reported in the Farsh Bazar area of central Delhi where Ajay lives along with his wife Ritu (30) and their two children, Vedika (9) and Krishna (8).
Ajay, who used to teach dance, yoga and aerobics in the locality, was for a long time caught in financial crisis, police said.
"Last night, at about 11 P.M., he dissolved Alprax in milk and gave it to his wife and children. As they fell unconscious, he slit their throats with a sharp weapon.
Before taking the step, Ajay sent an SMS to his brother- in-law Satbir, which was timed for delivery at 4 A.M. As soon as Satbir received the SMS, he rushed to Ajay's residence along with his wife even as the duo notified police about the case.
A police team reached the spot and took the family members to GTB hospital where Krishna was declared dead while Ajay, Ritu and Vedika were admitted in the ICU with doctors saying that their condition is critical.
