An insider said: "They know the sex of the baby but are keeping it private for now. They haven't picked out any names yet."
The news comes after it was recently reported Emma and Garrett were "surprised, shocked and happy" to be expecting a baby together.
Another source added: "[They are] surprised, shocked and happy at the same time, and so are their families."
Emma was first rumoured to be expecting a baby in June, and just a few days later, the news was seemingly confirmed by her mother Kelly.
When one fan asked on Instagram if Emma was pregnant, Kelly simply replied: "Yes!!" And when another said she would make "an amazing grandmother", she responded: "Thank you so much! Very excited."
Emma and Garrett were first romantically linked in March 2019 when they were spotted holding hands in the Silver Lake neighborhood of Los Angeles, and sources at the time said their romance was "casual".
An insider had said: "Garrett and Emma have been friends, but this is new, casual, and just a couple of weeks old."
The following month, sources again insisted Emma, 29, was "just having fun" with Garrett, 35.
Another source said: "Emma is newly single and neither she nor Garrett are in the right headspace to be in a serious relationship. They're just having fun hanging out and hooking up."