This might be a stupid question, but I wonder whether I should update the child theme as welL as the parent theme?
Also, when I uploaded and enabled the child theme something happened with the footer. One of the columns in the footer was placed above the other columns How do I fix this?
No, you don’t need to update the child theme. WordPress widgets configuration may be lost switch between different themes. Go to Appearance -> Widgets and add your widgets to widget areas.