San Diego here we come!!!
 

I am going to be traveling with 5 girls in January to San Diego and need some ideas on what to do!

We were in San Diego for two weeks in August. It was wonderful.
I would recommend the Hornblower Cruise, shopping at the waterfront shops of Seaport Village, going to the zoo, visiting Hard Rock Cafe, going to the aquarium in La Jolla (this is a really neat little place), and shopping and sightseeing in Old Town.

Live here and the whale watching is fun and it will be in full swing..
Go to the Birch Aquarium in La Jolla..walk along the coastline in LJ and see the seals at Children's Pool and have lunch on the terrace at George's.
Sea World or the SD Zoo is great and Balboa Park is gorgeous and it houses all the musuems..have lunch at the Prado.
Tidepools are fun by the pier in LJ or in Ocean Beach.
Ride the roller coaster at Belmont Park in Mission Beach and rent bikes and go all around from the bay to the beach.
Hike Torrey Pines Reserve on the ocean in LJ..
If it is close to the New Year, the Hotel Del will still have their decorations up and it is spectacular.
Coronado is a great quaint town and have fish tacos at the Brigantine across from the Del or all over SD.
Great seafood happy hour and the kids love it.

sdhe.com
aquarium.ucsd.edu
hoteldel.com
georgesatthecove.com
torreypine.org
belmontpark.com
brigantine.com

Wild Animal Park is our favorite in San Diego. You might even want to spend the night there or at the zoo. Roar and Snore. Be sure and do the caravan at the wild animal park where you get to feed the rhino's and giraffee.

AliAli, just to clarify, did you mean girls as in children, or a "girls" getaway?

You won't be able to get complete information here by just posing such a generic question. You should buy a guidebook or just print the necessary pages from www.frommers.com which is free. Then select activities that you would enjoy from those. Rent a car for SD.