Jamie Lynn Spears enjoys a low-key 17th birthday with Casey Aldridge

Jamie Lynn Spears spent her 17th birthday Friday night with just her fiance Casey Aldridge in Mississippi, while the rest of her family went out across the country in Brentwood, California

The pregnant actress reportedly visited a local Wal-Mart and Ruby Tuesday restaurant just outside Kentwood.

"They both seemed really happy, both in really good moods," a source says.

And while Jamie Lynn was quietly celebrating her birthday, big sister Britney, her brother Bryan and his girlfriend, mom Lynne and dad Jamie, dined with a group at Italian restaurant Peppone in Brentwood.

The was no talk of Jamie Lynn or the fact it was her birthday at the Spears family get together, an eyewitness says.

"Britney was beautiful and happy," adds the onlooker, who said she acted "very polite and composed.

"She was giggling with her friend and having a wonderful time."

Throughout dinner, the Toxic singer, 26, "was talking most to her brother Bryan, whom she seems to be close to. He seemed protective of her and shielded her from the rest of the restaurant."

After the meal, the family returned to Britney's Beverly Hills home.