Events with workshops

I have an events database that I now need to add workshops, the basic
structure of the tables is

Events:
---------
EventID

Attendee:
-------------
AttendeeID

Registration:
--------------
RegistrationID
EventID
AttendeeId

the real world situation is that some events we run have workshops, normally
the group will split into smaller groups and attend one of the sessions

e.g.
Bereavment
MCA
Cancer

Each event may have more than one workshop in a day, one workshop or none at
all. I have no idea how to design the table structure, do I need seperate
tables for Workshops, sessions. Any advice would be greatly accepted. If
you need any more info let me know

Thanks

Phil