Troubled pop star Britney Spears has put her custody battle with ex-husband Kevin Federline in jeopardy by taking their kids out of Los Angeles, according to reports. The 25-year-old flew to Las Vegas on Wednesday (25Jul07) in a private plane with kids Sean Preston, 22 months, and Jayden James, 10 months, after news of her erratic behaviour on a photoshoot for America's OK! magazine broke. Sources tell the singer made special arrangements to have her hotel room childproofed prior to her visit. Under California law, neither parent can take a child out of state without written permission from the other, or a court order. Sources tell People magazine Spears did not notify Federline - who is fighting for sole custody of the couple's children - of the visit, nor his attorney Mark Vincent Kaplan.