What can you do when grandparents, family or friends show favoritism towards one child over another?

It is natural (even for parents) to have favourites. As much as we could try not to have any preferences, it is kind of inevitable. That being said, being aware of this preference will help in reminding us to treat all our children the same (but please do not overcompensate and end up pushing away your favourite child!) Everyone's favourite may be different. Unless one child is noticeably getting a lot more attention over the other, there is no need to worry. Still, if you notice immediate family or close family friends playing favourites, you could let them know as they may not be aware that they are doing so. As soon as adults are aware of their actions, it is easier to consciously pay equal attention to both (or more) children.