If you see that they are in NotePad, then that means the leading zeroes are really there!
The issue is not with the file, the file is fine!
The issue is with how you are opening the files in Excel.
With CSV files, when you open them using Excel, Excel tries to determine what the format of each field is. Anything that contains all numbers will be treated as a number, so all leading zeroes of these fields will be dropped.
In order to open them in Excel and keep the leading zeroes, you need to invoke the Text Import Wizard so that you determine the format of each field and not Excel. There are two ways of doing that:
1. Change the extension of your CSV file to something like TXT
2. Open Excel (without opening a file), go to the Data menu, go to the "Get External Data" ribbon, and select From Text, and browse to your file.
In both cases, you need to go through each field. For the fields you wish to keep the leading zeroes, you need to select the "Text" Column Data Format in Step 3.