It is crowded, traffic could be bad. Restaurants are packed, you better make reservations. This town is a older community but you will see a lot of families during spring break. I don't think restaurants are kids friendly, for example, if you have little ones, you may want to bring their own cups, coloring books and crayons. A lot of families bring their own DVD player to entertain kids at the tables. I live here year-round and work for a restaurant on 5th Ave. I always see families come in. We are friendly and try to do anything in our power to satisfy our customers.
You won't see any wild behavior i don't think
Restaurants to go to? Truluck's, Chop's, Pazzo!, Yabba (family friendly until 10 on weekends, after that it's a club) Campiello's, Tommy Bahamas, Handsome Harry's, if you like chain restaurants you have from Carrabas to The Cheesecake Factory.
Good luck to you and have a great time here in Naples.