Menu button on iPad

Hello,

I have made my website with the theme Sydney: www.elpablocs.be. The menu button ‘Diensten’ had 2 submenu’s, ‘Web design’ and ‘Grafisch ontwerp’, but when I look to my website on an iPad, this button ‘diensten’ with the submenu doesn’t work. How can we arrange this that the submenu is shown?

Kind regards,

Pieter