There are tentative moves in Ireland to change the law so that more than two people can be recognised as the legal 
parents of a child. The Law Reform Commission, for example, has made a recommendation to this effect.
There are similar moves [1] in the US to break ‘the rule of two’. The ‘rule of two’ arises, of course, from a fact, namely the very basic fact that a child has two and only two biological parents. It can’t have more than two or less than two.
But another fact also exists, namely that a child through the course of its childhood, can have one, two or more parent figures involved in its life and when the number exceeds two isn’t it only right and fair that the third (or fourth or fifth person) is recognised as another legal parent with a legal right to a relationship with a given child, and vice versa?
And it is true, of course, that given the shifting and changing relationships of adults caused by divorce, separation and remarriage (or in many cases ‘re-cohabitation’ rather than remarriage) children can have plenty of parent-like figures in their lives as they grow up.
To a certain extent, but a very different extent, this has always been true. For example, grandparents often play a very significant part in the lives of their grandchildren (they have frequently lived or live in the same house as their grandchildren) but no-one has ever before considered them to be parent-figures as such to their grandchildren.
Indeed, as a direct result of the rise of divorce some lawyers are now calling for grandparents to be given rights of access to their grandchildren because in many cases, especially when their son has divorced and the ex-daughter-in-law has custody of the children, the paternal grandparents may only very rarely see their grandchildren in future.
What is being really highlighted here is the mess caused by rising divorce and separation. The proper solution to this isn’t to create third and fourth legal parents, but to reinforce and promote marriage, to reduce the rate of divorce and separation.
The answer certainly isn’t to break the rule of two which only adds to the confusion in a child’s life caused by divorce and separation and to potentially have more than two adults fighting over their welfare, not to mention the nightmare of potentially shuttling between not two different houses, but three or more.