The expectant mom enjoys steps out for some b-day fun.

Shopping at Wal-Mart and dinner at Ruby Tuesday were just two of the ways JAMIE LYNN SPEARS celebrated her 17th birthday on Friday, People reports. The mom-to-be was joined by fiancé CASEY ALDRIDGE, 18, for all the fun about and around Aldridge's home in Liberty, Mississippi.

"They both seemed really happy, both in really good moods," a source told the mag. "Jamie Lynn had a big smile on her face."

Of the couple's quiet dinner together, the source added: "They were like a little adult couple, very low-key."

Meanwhile, back in L.A., big sis BRITNEY enjoyed a meal out of her own, dining on Italian food at Ristorante Peppone with parents LYNNE and JAMIE and older bro BRYAN. The pop star appeared to be "in a great mood," a source told People.