get-childitem size attribute blank

I am having some issues with a powershell script that is really useful to identify unused documents.

get-childitem -path "\\server\share" -recurse | select fullname,name,attributes,lastwritetime,creationtime,LastAccessTime, size | Export-Csv C:\results.csv -NoTypeInformation

it works perfectly to produce fullname,name,attributes,lastwritetime,creationtime,LastAccessTime but size is always empty. I know in windows explorer it is also empty if I select size in the 'chose details' options, but if I right click say a file/folder I do see size/size on disc in the properties dialogue. is there anyway to tweak the script so it does pull in size/size on disc