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 People.com 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.