How to manage different iTunes Libraries from same computer

I have my own AppleID, iCloud account, iTunes Match account and my own Library.

But I have just one computer and one AppleTV.

How do I manage my granddaughters accounts, so they can listen to their own libraries on their iPod touch?

I don't want to mess up login to iTunes with another AppleID and then having to wait 60 or 90 days to log back int.