The children's mother and four other children escaped, WISN-TV in Milwaukee reported.

The victims were two sisters, ages 2 and 8, and their 9-year-old brother, police said.

Investigators suspected an extension cord with several devices plugged into it in a child's bedroom may have played a role in starting the fire.

Police said the mother's boyfriend was outside smoking a cigarette and tried to go back inside when he saw the fire but the home was quickly enveloped in flames.