how to handle directories with special characters in their name

I can't figure out how to recode the second clause of this function to handle directories like one named "[]"

function Get-DiskUsage {

  # parse and pray (but it does accept directory []
  # ------------------------------------------------

  dir |
    ? { $_.psIsContainer } |
      % {
          $size = ((@(cmd /c dir /s $_.name)[-2])[25..39] -join '')
          if ($size[14] -eq ' ') {
            $size = ' ' + ((@(cmd /c dir /s $_.name)[-2])[25..38] -join '')
           }
          $name = $_.name
          ' ' + $size + ' ' + $name
        }

  # object oriented, but it does not accept directory []
  # -----------------------------------------------------

  Get-ChildItem -Directory |
      Select-Object @{ Name="Size";
          Expression={ ($_ | Get-ChildItem -Recurse |
              Measure-Object -Sum Length).Sum + 0 } },
          Name

 }