Madonna's children want to out-do each other on her MDNA tour.

Lourdes, 15, and Rocco, 11, have been given jobs on her 86-dates of concerts with her daughter in the wardrobe department and son on stage.

However the relatives are apparently experiencing sibling rivalry.

A backstage source told the Daily Star: ''Rocco and Lourdes have developed a really competitive spirit as they take up roles on their mum's tour.

''Lourdes is in charge of fashion and wardrobe and is responsible for picking outfits for at least 10 of the dancers. Rocco is doing a series of breakdances and singing on a few tracks. Between the two of them, they are constantly involved in one-upmanship.''

The insider continued: ''Madonna has taken an army of helpers along with her for the children, including five nannies and eight private tutors.

''The cost must be absolutely phenomenal with their hotel bills, food and wages.''

The source revealed that the family spat is causing more stress for the 53-year-old star than the pressure of performing.

They added: ''It's all working out completely differently to how Madonna had hoped it would go and is creating family scenes.

''The kids are already causing her a massive headache and she had originally planned for her other two children David and Mercy to join them at some point. She's close to tearing her hair out.''