wp_nav_menu change sub-menu class name?

Question

Is there a way to change the child

generated by WordPress itself to a custom class name?

I know the parent

Answer 1

I had to change:

function start_lvl(&$output, $depth)

to:

function start_lvl( &$output, $depth = 0, $args = array() )

Because I was getting an incompatibility error:

Strict Standards: Declaration of My_Walker_Nav_Menu::start_lvl() should be compatible with Walker_Nav_Menu::start_lvl(&$output, $depth = 0, $args = Array)