Depends what you mean. Do you mean should mothers-to-be should wear cropped tops while pregnant? It's their body, and they are free to do what they want with it, so if they are brave enough to show their bellies while so large, more power to them. Now if you mean should they wear them after they have given birth, again, it's their choice. Frankly, with this weird trend of women wearing cropped tops without having their bellybuttons showing is annoying as hell. So if any woman, mother or not, wants to show her bellybutton, by all means, please do so!