Accessibility Improvement to Collapsed Checkboxes

Could you consider making the + sign next to a collapsed product category checkbox clickable by keyboard? The + sign can already receive focus (because it is a link) but the submenu can only be extended by clicking on the + sign with the mouse. It would be great if it could also be expanded by pressing Enter when the plus sign has focus.

Here is the element in question:

<a href="javascript:void(0);" class="woof_childs_list_opener" title="Сhild list opener"><span class="woof_is_closed"></span></a>

Thank you for considering!