Not too late at all but-
One parent one language at home- so if you're the native enlightened speaker you speak that exclusively and your partner is the Italian then they speak that.
Practice at home, get post it's and stick them on everyday items around the house
Encourage full spoken utterances and not single words. Model for her- so "drink!" Should be @dribk PLEASE, then on to I need or I want a drink please
The oxford university press has an online grammar section which is shorts excerpts, exercises and tests. Start on them at home with her.
Phonic patterns and spellings will be different, use the longman active study dictionary as a good learners dictiosnary and have her look up new words, define and translate them.
Read read read. In Italian and in English. Reading comprehension and inferentially skills are hard to teach but being an avid reader is the bedrock of this.
Usborne 1000 words is a simple picture distionary your younger child might like.
The British Council has lots of online games and exercises for your children to do.
Social language is apparent within 2 years and children will present with excellent conversational langUge and skills. Academic, sophisticated language skills take a further 5, and require lots of support.
If you're a motivated and engaged parent and the school is good, your children will do even better than their monolingual peers.