There has always been a nature vs nurture debate on how how children develop. In the main, it was thought that gender role behaviour was determined by social behaviour. However, a recent study of 200 children aged three and half shows that high levels of testosterone in the womb can cause girls to become tomboys. It didn't have any effect on boys. It's also believed that hormone levels in the womb can affect how a child's sexuality develops. So, yes, it is the mother's fault!