WPML allows you to add and customize language switchers to your site menus, widget areas, and footers. You can do this from the WPML → Languages page.
If you enable flags in the language switcher, you can also define their size.
In some cases, the size of the flags on the front-end might be different from what you set in the language switcher options.
This happens when a CSS style or a script in your site overrides the image tag styling and changes the flag size.
Such CSS styles and scripts might come from a theme or a plugin in your site.