Resolved Menu problem

Hi,

I have problem with off canavas menu, better say mobile menu. All items inside is always open, and i wanna to be open only main menu items not children.
you can see on this page http://rentaboat-trogir.com/novo/

Boats is main menu, and list of boats is childs, it is to big mess when it list it all togehter. I wanna some + or something on main menu item to expand child menus when client wanna do than, not to be open all time.

Tnx in advance