We'll be traveling to Messina, and staying there for about 4 weeks. While there, I want to take my son fishing.
Is fishing permitted in Passeggiata a Mare?
Is a license required?
Are there other places to fish?
I can say whay is required for italians, guess that for foreigners is the same.
For fishing in lakes and rivers (internal waters) you'll need a license that's not so easy to obtain for a foreigner on holidays (you have to pass an exam, and burocracy,...), so i don't raccomend you to choose a lake/river (and in Messina the best choice is the sea).
For fishing in the sea the rules are changing in this period, for sure until the end of 2019 you'll need a license that you can obtain with only a registration to the site of MIPAAF (ministery of forest-agricultural-alimentaty politics), free of charge. Here you can find the rules and here you can register, unfortunately the sites are in italian, i couldn't find an english version. After the registration, the confirm of registration is valid for fishing, bring it with you. You can't fish inside harbours and in particular areas where is explicitly forbidden (google "divieto pesa" - images for examples of signs, also signs with write "divieto di pesca") for some particular reasons.
My suggestion is, since you will spend quite a lot of time, to ask people...italians are usually friendly (particularly in south) and will help you. So for example ask a policeman (sure you will see some of them aroud the city), or even a weiter in the restaurant/bar after a dinner/coffee.
If you are particularly passionate about fishing, consider finding a fisherman that brings you out with the boat, this would solve also the license problem since you are with a local fisherman, a couple of hints:
Hope to been helpful.
Edit: consider also the fishermans village of Ganzirri, it's colse to messina (i guess you will have a car if you will stay there for 4 weeks), for sure less touristic, maybe here you can find a "true fisherman :)" that could bring you fishing with him, or a good spot for fishing, again...ask around :)