WASHINGTON — A child’s birthday is a time of joy for families. But for Troy Turner, of Clarksburg, Maryland, it’s a tough day to get through.

His youngest son, Jacob Hoggle, is turning 3 years old Friday. But Jacob and his 4-year-old sister Sarah Hoggle have been missing since September, and there hasn’t been a credible sighting of them since then.

The children were last seen with their mother, 28-year-old Catherine Hoggle, who has been charged in connection with their disappearance.

Hoggle, who suffers from schizophrenia, has been found not competent to stand trial and is being held at a Maryland psychiatric facility. Prosecutors say they hope that with treatment, she can be deemed competent and the case can move forward.

Turner, who has launched a massive search effort, has told reporters he believes his wife can tell police and prosecutors where the children are.

Montgomery County police have covered thousands of acres in their search for the children, and have asked homeowners to check their properties for any sign of the Hoggle children. The last search in April turned up no leads, according to police.

Find pictures of the children here and read more on the family’s website.

WTOP’s Kate Ryan contributed to this report.