Right now over 150 investigators are working to locate five-year-old Bri'ya and six-year-old Braxton Williams.
Police say they are now pulling surveillance video to look for clues.
Investigators have not ruled out foul play. They are also considering the children could have wandered off.
Over 150 investigators working to find missing Jacksonville siblings
The search is expected to resume Tuesday.
Some parents News4Jax spoke to say they’re fearing the worst; that the children could have been abducted. In a Monday afternoon press conference,
Jacksonville Sheriff Mike Williams said searchers “have found nothing.”
Search for missing children nears critical 48-hour mark
Searchers are looking everywhere at one point focusing on a wooded area just north of the west Jacksonville neighborhood.
The kid's grandmother said she doesn't think that is an area they would visit.
"Never knew them to go in there, I just don't think they'd go off there. I just hope no one took them," Lloyd said.
The sheriff stressed that with nothing to go on, not a witness or anything captured on surveillance cameras, they must consider any and all possibilities.
"Abandoned cars, we have a significant number of abandoned trailers in this complex, they are 5 and 6, so if they did walk away, think about that, but anything in the area that we would attract kids to play, we're looking at that."
Children at center of Florida Amber Alert now missing for 3 days