The best way for a child to learn a foreign language is to be exposed to their different sounds, rhythm, and tone right from birth. It may be surprising, but babies are able to recognize and distinguish them even before capturing the meaning of words and sentences: the process for acquiring a second language is similar to that for the mother tongue.
The earlier a child is exposed to a foreign language and the easier it will be to learn it naturally. Children can learn easily and naturally in a few months what an adult will never be able to do, because this incredible ability to absorb starts decreasing after early childhood.
It is a well-known fact that born from parents with a different nationality children have no problems in learning different languages. And in order to offer this chance also to monolingual children, you can, right from the earliest days, let your children play with toys that allow them to play both in Italian or in a foreign language. Listening to nursery rhymes, short sentences, and songs in both languages helps associate terms, tones, and expressions in an easy, natural, and fun way.
Let's not forget that being exposed early to a wide and differentiated range of sounds will make learning (and not only language learning) much easier and flexible.
More importantly, knowing more than one language is an essential resource for children who, in the future, can easily interact with different cultures and open up to the world.