Things to see and do:
A horse drawn carriage tour. These leave from the City Market area, which is an attraction in itself. The drivers/guides are excellent; they must pass a test in Charleston history in order to be licensed.
For a taste of history that your kids will enjoy (at least mine did) check out the Old Exchange and Provost Dungeon. Here's a link for some info:
http://www.oldexchange.com/
I second the vote for Patriot's Point. It's very interesting and the kids enjoyed it (always a big plus

) It's located in Mount Pleasant just across the Cooper River. Here's their website:
http://www.patriotspoint.org/
There is a great new aquarium in Charleston, right on the Cooper River next to the Fort Sumpter tour departure point and the Charleston IMAX theatre. Read about it here:
http://www.scaquarium.org/
Lastly, I highly recommend Charles Towne Landing which is 10 miles north of the city on the Ashley River. It is the site of the original city from 1670. (It was moved 10 years later to its present site.) It is a beautiful park setting, again my kids love it. Rent bicycles there and enjoy it up close. Info on CTL is here:
http://www.discoversouthcarolina.com/stateparks/parkdetail.asp?PID=1575
For other general info, here's the link to the Charleston Visitors Bureau.
http://www.charlestoncvb.com/visitors/index.shtml
I can't help you out with hotel recommendations as we usually just drive up for the day (it's a little less than two hours away for us) but I can recommend a few restaurants. We have eaten at and enjoyed 82 Queen (my personal favorite), Magnolias, Poogan's Porch, California Dreaming and Sticky Fingers. Most of these have links to their websites on the visitor's bureau website I posted above.
Charleston is a wonderful city, I'm sure you'll all love it.