Going north from Ft Myers Beach you have lots of interesting stops on Sanibel, Captiva, North Captiva and Cabbage Key. All are within 1hr of FM Beach and are accessed from intercoastal.
North from there you have Charlotte Harbor with ports like Burnt Store Marina and Fisherman's Village at Punta Gorda about 2 hrs. from FM Beach.
If you go out Boca Grande Pass you can run north to Venice 1.5 hrs, Sarasota 2hrs and Tampa Bay, St Pete's and Clearwater about 3hrs.
I'm sure others will jump in and mention some of their favorite FL west coast spots.
Hope this will be a little help.
Good luck and it will make a great family trip.
Don't forget your charts and pick up a cruising guide.
Bob