Italian:
My son is allergic to...
Il mio figlio e allergico a (latte, noci, whatever - make sure you know the words).
Italy is pretty good but people don't speak much English outside tourist areas.
Packaging is fine if you know the right words, they follow the EU labelling system. Sweet things are very difficult - most biscuits have egg and nut - so take your own. In ice cream shops, he may be able to have the sorbets but check carefully. Eating out, it really helps if you know what is likely to cause a problem - for example, pizza dough is almost always fine for us.
Ordinary pasta should be fine.
Bring all your medicines, make sure you have your EHIC cards, and work out an emergency plan (emergency numbers in the country, how to ask for a doctor, how to ask for an ambulance). I have used the Italian health service with my kids on various occasions and it's pretty good.
We travel with my DD who is egg and nut allergic. She has had reactions on holiday (in France we discovered she was allergic to prawns, and this year in Italy she ate a nut) - it is a less controlled situation so if you can bring stuff, swot up and know what to do in case of a reaction, you should be fine.