I don't know whether it is common desire in 'onlies', but I was desperate for a brother or sister and this feeling only seemed to intensify as I grew older. It is only now in my early thirties that I am finding some self-acceptance about not having brothers and sisters. I do admit to still having a slight envy at 'big' families; siblings, cousins, nieces, nephews. In fact, even as I write I feel that tinge of sadness about the fact that I will never have a brother or a sister. I will never have that experience of a shared childhood and the knowledge that someone knows your past. It was definitely a grieving process for me, going through the painful feelings of loss and loneliness to finally accepting what I have here in this life.