I know someone who did this and went to India for 6 months.
They had long discussions with the school who were very supportive. They couldn't hold the places, but promised to do all they could to get them back in.
They penpalled the school while they were away and gave a presentation when they came back.
So, I would say talk to the school, a lot will depend on where you are and the pressure on school places.
Do they speak fluent Italian? I would think this would be an absolute must before moving. It is a tall order for any child to relocate and not understand the language.
This is, I'm afraid, poor advice. I work with a lot of families moving to and from the UK, and while it is great to have lessons to get a head start, the best way to learn the language is full immersion in school. Be warned though, it isn't easy, especially the first month, and not all kids will be 'chattering away' after 3 months. I would say, working functional language after 3 months, fluent at 6 and native speaker level at 12, if it is English to European language. If it is Russian/Chinese or a tonal language, double or triple those times.