Problem resolved!
I’ve created a footer.php in the child theme and then the menu didn’t work proprerly, I don’t know by now the reason.
When I’ve deleted footer.php the menu drop down in mobile…
Thank you Media X!!!
In Appearance-Menu I’ve created a specific menu to be shown.
In twenty twelve it works but when I set the child them, it doesn’t.
I have (I think) a similar problem.
I’ve created a main menu in the widgets area and it works fine, but when I see the blog in mobile, the menu doesn’t display (drop down)…
I haven’t changed anything about navigation in my child style… Anybody can help? Thank you!!