Pop queen Madonna is so busy that even her children have to take an appointment to spend time with her.

The 52-year-old singer has been juggling with responsibilities of being a mother, a singer, director, attending Kabbalah meetings and managing her $354.66 million fortune.

Insiders say that Madonna's children Lourdes, 13, David, 4, Mercy, 5, and Rocco, 10 have to book 15-minute slots to see her. She gets her assistants to write in her diary "time with David", and "time with Lola (Lourdes)", dailystar.co.uk reports.

Mercy was recently seen clinging to Madonna as she shot for her latest directorial venture "W.E." in London this week. The film is about the affair between King Edward VIII and American divorcee Wallis Simpson.

Madonna helps all her children with their homework, singing lessons and cooking, but only if it has been planned in advance.

"Madonna loves her kids, no one doubts that. But being an international megastar means there just aren't enough hours in the day. They've adapted, though," said an insider.