Anna and Josh Duggar and their newborn son
06/15/2011 at 11:00 AM EDT
The Duggar family just got even bigger – it's a boy for Josh and Anna!
Josh, 23 – the eldest son of Jim Bob and Michelle Duggar – and his wife welcomed a new addition on Wednesday, four days earlier than expected
, a source confirms to PEOPLE. The couple are not ready to release the name publicly yet, but they are staying with the "M" theme.
Weighing in at 8 lbs., 5 oz., he joins big sister
MacKynzie, 20 months. And he'll have plenty of doting relatives with 18 aunts and uncles – Jim Bob and Michelle's children – whose lives are documented on TLC's 19 Kids and Counting
Anna, 22, gave birth at 5:55 p.m. in the family's Tontitown, Ark., home, the same place MacKynzie was born.
The newborn will also have a very special playmate: Michelle's youngest, Josie, who was born very premature
, is now a healthy 17-month-old
"I think of Josie being born at only 25 weeks," Josh told PEOPLE prior to the birth, "and it makes us think about how precious life is and what a blessing each child is."
For more on the latest Duggar addition, tune-in to 19 Kids: First Grandson
this Sunday at 8/7c on TLC.