The pop star, joined by her brother Bryan, flew in a private plane to Sin City on Wednesday afternoon with kids Sean Preston, 22 months, and Jayden James, 10 months.
No word on what, exactly, Spears plans to do while in town, but sources tell PEOPLE she went to dinner at the Country Club at the Wynn Las Vegas. She also made special arrangements to have her hotel room childproofed for the visit.
The trip could also pose some problems for any custody battle with ex-husband Kevin Federline: Under California law, neither parent is allowed to take a child out of state without written permission from the other – or by obtaining a court order. According to a source close to Federline, Spears failed to notify her ex or his attorney, Mark Vincent Kaplan, that she was taking the children to Las Vegas.
A lawyer for Spears did not respond to calls for comment.
• Reporting by JENNIFER GARCIA, MARK GRAY, MARY MARGARET and FRANK SWERTLOW