For a basic overview of city museums and sights you can visit this site:
http://www.saint-petersburg.com/very basic in fact and not includes some interesting places to visit in the city but gives overall impression of local sights.
Also you can use this site for basic museums info:
http://www.russianmuseums.info/piter.aspIf you are interested in military history than i can recommend these places to visit:
http://www.russianmuseums.info/M153http://navalmuseum.ru/ (museum site in Russian)
Central Naval museum, has a nice collection of models, art, weapons and other fleet related things.
http://www.russianmuseums.info/M108http://suvorovmuseum.ru/ (in Russian)
Some nice art and weapons and a whole lot of various tin soldiers.
http://www.russianmuseums.info/M152http://www.artillery-museum.ru/en/home.htmlMy personal favorite place.

Has some interesting military vehicles, cannons, hand guns, and other military thingies. Also a place where some interesting foreign military-historical exhibitions are usually shown.
Located very close to Peter and Paul fortress by the way so you can visit both places in one go.
I`m not sure if i can really help you with restaurants as i`m much more frequent visitor to pubs than restaurants.
But for family visits we normally visit some of these:
http://en.ginza.ru/spb/restaurant with "Mamaliga" being my favorite one.
If you find something useful from my info and will want more information about directions or basically anything related to St.Petersburg you can PM me and i will try to help you with it.