Maddie Briann

Maddie Briann entered the world with a full head of hair, her daddy's toes and the world's most famous aunt waiting just outside the door.

New mom Jamie Lynn Spears, daddy Casey Aldridge and baby Maddie are catching up on rest following the birth Thursday at a hospital in McComb, Miss., near the Spears family home across the state line in Kentwood, La., a source tells PEOPLE

"They're doing terrific," the source says. "The baby's got 10 fingers and 10 toes ... and a full head of hair. She's long, a tall baby, and she weighs 7 lbs, 11 oz."

When the baby was born at about 9:30 a.m., Jamie Lynn's sister, Britney Spears, and the rest of the Spears and Aldridge families were just outside the birthing room in the spacious maternity suite.

The relatives then joined the new family in the birthing room and took turns holding Maddie Briann and commenting on her features. When new grandmother Joyce Aldridge held the baby, she remarked that Maddie "has Casey's toes," the source says.

Jamie Lynn, 17, and Casey, 19, intend to get married soon, but no date has been announced. Jamie Lynn recently purchased a home in nearby Liberty, Miss., where she and Casey have been living for about three weeks.