bigger focus lines

I would like if the focus lines that indicates where I am when I use the tab
key to navigate on the desktop, in Internet or in PowerPoint were more
contrasting. For now, they're just little dotted lines. Is there a software
or something that would give the option of choosing the tickness and the
color of the lines ? I work with children that have multiple disabilities and
this would be very helpful.

Thank you for your help.

Christine./