The man was taken in for questioning around 2 a.m. Wednesday at a Placer County Denny's restaurant after authorities spotted a white Chrysler minivan missing from the scene of the killings outside.
Sacramento County Sheriff's spokesman Jason Ramos says the man was believed to be in possession of the van.
He was being interviewed by homicide investigators. The woman was in her 20s. She and her 2-year-old son and 3-year-old daughter were found dead by the children's father on Tuesday afternoon at their Rancho Cordova home.
That's about 15 miles east of Sacramento.
Authorities have not said how they were killed, although Ramos said they suffered a lot of trauma.
(Copyright 2012 by The Associated Press. All Rights Reserved.)