My dear aunt lives in Utah and comes to her homeland Georgia about once a year, and has brought her large family posterity with her one year on caravan. For the culturally curious family with an interest in gardens, history, architecture and art, Savannah is a wonderful place to walk and explore. The new Jepson Art Museum has a wonderful children's component, ArtZeum. On occasion, the Mansion at Forsyth Park offers children's cooking classes. Dolphin exploration, Tybee Beach fun on the Atlantic Coast, a stopover at Fort Pulaski, feeding squirrels and flying kites in Forsyth Park, and discovery using the "Savannah Safari" coloring book ... a book that finds dolphin downspouts, lion water fountains, etc., make an educational, fun adventure. Then travels south on Highway 17 to discover the Liberty Trail, an exciting Revolutionary War trek. (Liberty Trail brochure at Exit 13 off of I-95.)

Geez, Boston - now you're talking!!

Boston has amazing history, and it is safe and really interesting... from the North Church, to downtown streets which are really narrow because there were no cars back in the days when they were first plotted.

Might be a good idea to stay in some outlying area because Boston hotels are among the most expensive around.

Southern Utah to Boston makes for a great trip... eventually.

Maybe Boston can still be considered. Check flights to MHT (Manchester NH) or Providence. You don't need a car in Boston and you should be able to get some kind of shuttle transportation between the airports. MHT is less than an hour from Boston's Logan. But weather could be real iffy in March.
Have you considered Charleston?

So Northwest Male you never did explain "Philly has the history... but wow" comment.

Philadelphia is a wonderful city to visit. Small walkable downtown area, great restaurants, world class museums, interesting historical sites etc.