I was passing through immigration in Heathrow T3 last year and the immigration officer challenged a woman because her toddler had a different surname. I know several women who have kept their maiden names but whose kids have their husband's surname. What was she meant to do, ask for a DNA test?
This could have been ignorance on the part of the immigration officer. There are countries, Spain eg, where women do not take their husband's surname. Multiple surnames are the norm, children's surnames are in the order, father's 1st, mother's 1st and so on. The child's passport would therefore show the father's surname followed by the mother's.