I think the person who will undergo for plastic surgery for cosmetic or to make them looks pretty, will just confuse their future partner and kids about their looks. Specially their partner, they might think that there's a 3rd party on their relationship, because their kids looks different. LOL.
This is funny and at the same time an important factor especially for those that are yet to get married. I mean that you may get married to a fair person and if you are unaware of the surgery that they undergone, you are likely to get confused when the matter is at hand.