Hi Kathy and welcome to our community! New entry regulations here in Italy that go into place on March 1 no longer require testing for passengers arriving with a valid vaccination or recovery certificate. Since you've all had a booster, that means your vaccination certificate here in Italy has unlimited validity - no expiration date.
Have a wonderful trip, and let us know if there are any other questions regarding your Italy travels that we can assist you with! Buon viaggio!
PS A negative test is still required to re-enter the US - more information at the US Embassy in Rome Covid-19 page here48.