Kevin Federline's lawyer says it's not certain that Britney's children are going on tour.

Mark Vincent Kaplan has revealed that an agreement is yet to be reached on whether three-year-old Sean Preston and Jayden James, two, will go on the road with their mother.

He said: "There can be an agreement reached in probably the next day, but there is not an agreement that is signed yet."

Britney's 'Circus' tour is due to kick off in New Orleans on March 3, but the 27-year-old singer has reportedly threatened to cancel if her boys are not allowed to join her.

Kaplan continued: "Kevin is working to make them accessible by going on various central locations in various areas of the country. He is doing that because he wants her to be able to have the maximum positive environment around her to assure the tour will be successful."

Even if an agreement is reached, Kaplan says the boys will not attend the shows, but will be "available" for the singer on "pretty much the same schedule that she has now".

It is not clear whether Kevin's girlfriend Victoria Prince will be joining the tour party.

Kaplan said of the former professional volleyball player: "She is very solid, responsible, and has a very positive effect."