Breakfast recommendation in Frankfurt?

Hi all. I have a layover with two older family members en route to India. Arrive FRA 6am - Leave 1:30pm.

I looked up taking the train into town, and a few sites recommended the S8 or S9 to Hauptwache.

Any recommendations of a German restaurant that's open early for a good breakfast? And also spacious/large enough we wouldn't be in the way with our bags, and wouldn't hog a table if we spend a hours with coffee and relaxing after eating, or maybe one of us sit while the other explores a few shops. (Not sure about bag storage at FRA, but we travel fairly light and have simple rollerbags.)

Or any other station/platz would be nice, (just prefer no transfers) -- and somewhere to spend a few hours and give a quick taste of Germany, since we'll have the opportunity be nice to give my family a quick taste. I've been to Munich/southern Germany myself before but never Frankfurt.

http://www.frankfurt-airport.com/content/frankfurt_airport/en/checkin_luggage/luggage_neu/storage.html there is luggage storage at the Airport, get off at the Hauptwache instead the main train station, from there you can have a short stroll to the Roemer.

Cafes should be open that early, some bakeries offer cafe also, but often only have stand up tables.

Buy this ticket from the machine at the airport http://www.rmv.de/en/Fahrkarten/Die_richtige_Fahrkarte/Fahrkarten_im_Ueberblick/Tageskarten/42090/Gruppentageskarte.html make sure you have some small € bills, because the RMV machines don't take cc to my knowledge, also plan on paying your breakfast in cash, smaller places will not accept cc's.

Easiest to reach, and open that early, is the food court inside the main train station in Frankfurt (Hauptbahnhof). It is where you will arrive in the city when coming from the airport.
There are food stalls for a variety of tastes including tipical German food. They also have tables where nobody will bother you. However, if some family members want to sip cofffee while others go look at shops, a better place for that would be a cafe / bakery near Hautpwache / Römer. The thing is that shops dont open until 9-10 am so maybe take a breakfast first, then move on to the shopping area.

I would recommend using the bag storage at the airport and not going into the city with large bags, They would be a hassle. The train station has bag lockers, but the airport also has, and at the airport the service is more user-friendly.

Thanks very much and for the luggage link. If the bag storage at FRA is safe and secure I'll plan on that - will make it easier to walk around.