A 4-year-old boy was killed and three others, including his parents, both labourers, injured when the basement wall of an under construction building collapsed here, police said on Saturday. The incident took place in Sector 63 on Friday. "An FIR has been filed," a senior police official told IANS. Those injured include Prakash and his wife, who were working as labourers at the site, while their son, who was also near the wall, died. The third labourer has been shifted to AIIMS as his condition was critical. "We are investigating the matter," the officer said.