Powershell doesnt shows else condition when get error

Since Get-ChildItem throws a terminating error when the folder path does not exist, the function will end there and the rest of the elseif or else conditions are never executed.

I would suggest doing this in a try{..} catch{..} so you can capture exceptions like that:

Something like

function listChildFolder {
    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [string]$folderPath
    )    

    # capture the terminating error message when the path does not exist
    # by specifying -ErrorAction Stop
    try {
        # since we do not add switch '-File' or '-Directory', 
        # the Get-ChildItem cmdlet will return both types
        $filesAndFolders = Get-ChildItem -Path $folderPath -ErrorAction Stop
        # next, find out if we found any files or folders in the path
        # the '@()' forces the $filesAndFolders variable into an array, so we can use the .Count property
        if (@($filesAndFolders).Count) {
            $filesAndFolders | Sort-Object LastWriteTime -Descending | Select-Object Name
        }
        else {
            Write-Host "No files or subfolders found in '$folderPath'"
        }
    }
    catch {
        Write-Warning "Error: $($_.Exception.Message)"
    }
}


$folderPath = Read-Host "Please enter a folder path"
# call the function
listChildFolder $folderPath

^{Another recommendation is that you use the PowerShell Verb-Noun naming convention for your function}

As per your comment where you say you may not use try{..} catch{..}, there are other ways of course.

How about this:

function listChildFolder {
    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [string]$folderPath
    )    

    # test if the given folder path exists
    if (Test-Path -Path $folderPath -PathType Container) {
        # since we do not add switch '-File' or '-Directory', 
        # the Get-ChildItem cmdlet will return both types
        $filesAndFolders = Get-ChildItem -Path $folderPath
        # next, find out if we found any files or folders in the path
        # the '@()' forces the $filesAndFolders variable into an array, so we can use the .Count property
        if (@($filesAndFolders).Count) {
            $filesAndFolders | Sort-Object LastWriteTime -Descending | Select-Object Name
        }
        else {
            Write-Host "No files or subfolders found in '$folderPath'"
        }
    }
    else {
        Write-Warning "Error: '$folderPath' does not exist"
    }
}


$folderPath = Read-Host "Please enter a folder path"
# call the function
listChildFolder $folderPath