Boston, MA is a great place to take visitors whether they are from the US or abroad. Depending on the time of year that they visit, different options would rank higher.
For example, if they arrive in the warmer months, say May to September, then an excellent place to start would be the freedom trail. This is a marked track that follows the famous ride of Paul Revere as the British forces arrived in Massachusetts Bay prior to the war of independence. During the warmer months, this path is nice to walk along as it will take your family along the landmarks of Boston, through the Boston Common, past the Quincy Markets, the Bunker Hill memorial, and through Boston's North End where some of the best Italian restaurants in the country can be found. In addition to this, Boston is home to two of the most prestigious universities in the world, Harvard University and the Massachusetts Institute of Technology. Free walking tours are available on both of these campuses which are located on the other side of the Charles river in the city of Cambridge. You can also go to a baseball game at the famous Fenway Park stadium to see the local team, the Red Socks play, as well as enjoy the city's shopping district along Newbury St. and the Prudential.
If, however, your family visits in the colder season, or worse during the peak of winter, Boston still has plenty of fun and enjoyable activities. You could take them to an ice hockey game at TD Gardens to watch the local team, the Bruins play. There are also Christmas and winter markets in the Sea Port district throughout the holidays. For skiing, the mountains of New England are within a few hours drive and are often excellent for new and experienced skiers.