70-200 @ f/8, against a white wall with soft light from both sides of the subject....
When I was taking my baby's photo for his passport at 1 month old, I found the minimum focal distance of the 70-200 too great. A ring flash was great for even illumination.
I used the 100L + MR-14EX flash, with the baby lying on a white towel on the floor. f9 and 1/100th. The mistake I made with the first couple were not leaving enough space to allow cropping to size with the eyes on the right line. It actually worked better when I took in landscape rather than portrait, and cropped to portrait.
Attached is the photo we used. Not a great photo, but meets the exacting requirements for an Irish Passport.
(ps my baby has been on a Ferry, but not on a plane.....)