Montgomery County sheriff's Lt Scott Spencer said the children ranged in age from 6 to 13 years and that their bodies were found amid the debris of the home.
"We've moved from a rescue operation to a search and recovery," he said.
The three critically injured people included a 10-year- old boy who suffered severe burns.
The flames and heat drove away emergency responders who attempted to enter the home near Conroe (KAHN'-roh), about 40 miles north of Houston, Montgomery County Fire Marshal Jimmy Williams told KHOU-TV.
Three other members of the family were taken to hospitals with injuries that are not life threatening.
The flames spread to two adjacent homes that sustained minor damage, Spencer said.
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