Having 2 biological parents or not. Is it that simple?!

To start with, the aim is to criticise "what marriage is for" text. Eventhough it explains the definition of marriage in many ways and same-sex marriage; especially there was also another paragraph ,which considered parent-children subject, stuck in my mind at first sight. Gallagher demonstrated Child Trends research in the text was that having two biological parents provide children to have better life and not to face higher risks. To what extend having a better life? What is the age range for those affected childrens? What about the children who have to live with one or none of their parents? Don't you think their life goes well either? Well i need to say that most of my friends haven't lived with their 2 biological parents for a long time, so do i. Maybe some doesn't lucky like me, i am pretty sure they have problems at first. But nowadays children after a certain age realized divorce or death are not the end of the world. What i am trying to say is that when there is a research on that issue, it must be based on a certain age (e.g. children 5-10 year old) and should be updated. However, when the generalization turns into overgeneralization, nothing really seems reliable.