"They both seemed really happy, both in really good moods," the source tells PEOPLE of the couple's outing near Aldridge's home in Liberty, Miss. "Jamie Lynn had a big smile on her face."
Spears, who is pregnant with Aldridge's child, took in a quiet dinner with Aldridge, 18, at the restaurant.
"It was just the two of them," says the source. "They were like a little adult couple, very low-key."
They then went to Wal-Mart, where Spears looked at sleeping bags. Jamie Lynn recently has been flashing a big ring from Aldridge. They are expecting their baby this summer.
Meanwhile in Los Angeles, Jamie Lynn's big sister Britney Spears gathered with the rest of the Spears clan for a family dinner in Los Angeles.
Britney, parents Lynne and Jamie and brother Bryan joined a group of about 10 people for an Italian feast at Ristorante Peppone in Brentwood.
She (Britney) was in a great mood, and had dinner with her family and friends," a restaurant source says.
Additional reporting by PERNILLA CEDENHEIM
Reporting by MARK LAMBERT
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