So we are looking for FL beaches with boardwalks or plenty of other stuff for DD and I to do.
I've never seen a beach in Florida that had a real NE-style boardwalk such as you might find at the Jersey Shore. The truth is that in Florida most people value the opposite in a beach; the less developed the better. The point for most folks is to either swim, snorkel, play in the sand or surf-cast.
At the very least you'll probably find the amusements on the opposite side of the coast road, so that you have to cross traffic to get to them from the beach itself.
Are you driving, and how long do you have? I ask because in March, you'll need to be pretty far south to actually get into the water; probably no further north than Ft. Myers or Palm Beach. Those communities are WAY south of Orlando; most people fly from Orlando if possible. On parallel with Orlando or north of it the water is going to be no warmer than about 70F in March; too cold to do more than wade for most people.
If you want shopping, then the area around Ft. Lauderdale and Palm Beach is probably your best bet. Palm Beach has some of the most exclusive boutiques on the East Coast, along Worth Avenue.
http://www.worth-avenue.com/ For folks with less rarified tastes, there is also Sawgrass Mills just outside Ft. Lauderdale; it is the world's 4th largest outlet mall, and also contains a nice children's museum called Wanadoo City.
The only Florida beaches I have been to that have a whole lot of other amusements within a couple of blocks have been Ft. Myers, the north end of Daytona, and Panama City. I'm sure there are others, though; because I admit that I rather hate kitschy beaches -- I prefer the sort that have no businesses at all, where all you can see for miles is sand and sea.
What kind of fishing does your DH plan to do? Different areas specialize in different types of angling and different species of fish. If he is after Tarpon, he'll want to be down in the flats near the Keys at that time of the year, they migrate through the Keys in March. (If you don't fish, I should tell you that Tarpon are not edible. Enormous, and a great challenge to catch, but they taste like a bottle of rancid oil. No one will ask you to clean one for dinner.)