Construction is good and so is Habitat for Humanity.
I would also say your son should look for internships in different areas (if he/you can afford a room to rent). If you live in the DMV, your kid needs to look outside DC, NYC, Boston, etc, and look at internships at smaller less popular cities.
My cousin is a sophomore and I told him to do the same thing (he is an econ major) as the finance internships for next year are very competitive.
Amtrak has an internship in Philadelphia
https://careers.amtrak.com/AMTRAK/job/Philadelphia-Summer-2024-CivilFieldHeavy-Construction-Engineering-Intern-90353303-Philadelphia-PA-19104/1103023100/?utm_campaign=google_jobs_apply&utm_source=google_jobs_apply&utm_medium=organic
DOT also has internships.
Have him contact career services at his school and ask about engineering internships. Probably better to see if their is a career person in his school rather than the entire university since they should know better where to target for an internship. If not, maybe he can ask upper class people if they have any ideas.
Good luck!