A simple statement that affirms your support overtly may be an important understanding for your son or daughter. Ask them what they are doing rather than how. It is a subtle difference that conveys your interest without sounding evaluative. You might think of ways they are successful at getting rid of stress and make suggestions that they engage in positive activities that have worked in the past. Sending a picture of a family vacation, or favorite haunt from the past could be helpful.
College is packed with many stressful experiences and having support on reducing the load can help.
Students often think they should be studying all the time they are not in class. You might help with contacts in a wide range of areas that will help your sons and daughters look at the working world through experiences. We know the more students use the resources of the university the more likely they are to persist through the hard times and be successful in their next transition to graduate school or to work. Get them to use the faculty and TAs during office hours. Being part of the campus community is very important to developing self-confidence about education.