PASADENA, Texas -- A mother issued a plea for someone to return her missing 3-year-old daughter and 7-year-old son who disappeared from a Pasadena apartment complex, KPRC Local 2 reported Monday.

Pasadena police said 3-year-old Denim Sylvester and 7-year-old Randy Sylvester Jr. were last seen at a complex at 4025 Burke Rd. at about 2 p.m. Sunday. Their family reported them missing at about 9:15 p.m.

Investigators said both children are black.

Denim is 2 feet 5 inches tall, 35 pounds and was last seen wearing a pink V-neck T-shirt with brown trim, pink shorts and pink flip-flops. Her hair was braided with a pink ponytail.

Randy is 4 feet 1 inch tall, 55 pounds and was last seen wearing a blue and orange Florida Gators shirt, blue denim shorts and blue and white tennis shoes.

"Whoever or whatever, if you know where my kids are, return them to me," the children's mother said. "That's all I want you to do is return them to me. Whether you drop them off by the freeway or whatever, return them to me."

The children were last seen between the apartment complex's tennis courts and the swimming pool, investigators said.

Detectives sifted through the children's mother's car looking for evidence and went door-to-door with a photo of the children to see if anyone had seen them. Volunteers sifted through Dumpsters looking for clues.

Police said they interviewed the parents for several hours and found inconsistencies in their story.

"I can't be specific about what that is," Capt. Bud Corbett said. "The conflict does exist and we're trying to sort it out at the moment."

But police said the parents are not considered suspects.

Neighbors said Randy liked to play outside, but Denim kept closer to home.

"Randy's outside all the time," resident Stacy Jump said. "The little girl, I see her playing on the steps and stuff, but I really don't see her playing outside much. That's why it's really weird to me that she's gone, too."

Residents said they are frightened that someone may have come into their community and hurt the children.

"It makes me nervous," one mother said. "Someone could have picked them up. Anything could have happened to them. My kid's not that old. Still, if my kid was missing for that long I'd be going crazy."

A Fort Bend County K-9 unit is helping in the search. Officials hope bloodhounds will pick up the children's scent and track them down.

Anyone with information about the children's whereabouts is asked to call the Pasadena Police Department at 713-477-1221.