Well, it ALL depends.There ARE families where parents have multiple children, their love increases either between or among each of their children.They treat all their children as if they are special and precious God-entities.Such parents practice no favoritism and all their children receive the prerequisite parental time and attention.However, such parents are very few and far between.
In the average multiple child household, parents are apt to love some children more than they do others.It also depends upon myriad factors & variables in the parent-child dynamic.Such factors and variables include parental personalities,favoritism,family size, & birth order.
There are parents based upon their own individual personalities love one child over another.The child may have a personality similar to the parents. He/she may have a talent that the parents find admirable.Parents also tend to love some of their children more than others if the latter is aligned with the particular family consensus.Parents also love one child over another if he/she is deemed more compliant/managable in the parents' eyes.Children who have personalities/characteristics that are different/opposite from their parents seem to be less loved by their parents as they are deemed difficult.
Then there is the taboo issue of parental favoritism.The majority of parents practice favoritism although they are loathe to admit it.There are children who are loved,receiving preferential treatment over other children.Reasons for parental favoritism includes similiarity of personality,beliefs,& interests, even birth order.The favored child may have something that the parents adores opposed to the other children in the family.
Then there is family size.In smaller multichild families, all children are more or less treated equal.They all receive individualized parental love & attention. However,in large/very large multichild families, oldest/older children tend to be discarded, being cast aside in favor of the younger siblings.In large/very large multichild families,oldest/older children raise themselves as the parents believe that the latter DON'T need them so much. In such families, it is the YOUNGER/YOUNGEST children who are lavished w/parental love & attention.
The issue of birth order can be correlated to family size or not. Usually oldest/older children are expected in many families to be on THEIR OWN at an early stage.It's the youngest/younger child who receives IT ALL.