Um, they sound like they are actually quite smart kids -- engineering and biology. I think these kids will be nice about it and probably are more nervous about their new school than you are to call them.
I got alot of these calls from the University of Iowa (it came down to Iowa and Michigan State for me). They would ask if I had any questions, I'd say nope...and they'd reply that if I did, drop them or Iowa an email (or something like that).