If parents have more than one off-spring,does it really differ?

A critical question, hammering my mind since long time. The question, I asked many(as I'm Alhamdollilah a single child & thus doesn't experienced such)& believe me, answer differed with person to person.
Some said straight-forwardly, parents does not differentiate & dicriminate between any of their children but there are some realistic people, including my papa, that usually this extreme discrimination doesn't takes place between their children, yet a little extra favour to any one may occur. This answer was quite interesting for me, & pleased my heart as I also believed it.
But as moving forward, when I asked my grandpa about it, he out-rightly answered,"yes! Differences do occurs. Parents are more likely to shower love care affection & importance to those children of their who has some talent & capabilities. If they are dull or incapable of achieving something in life or doesn't seems to be having a bright career & future, then parents doesn't have any favour sympathy & love for them. Moreover, a disobedient child is more likely to cut-off his/her parent's tenderness, optimistic emotion & kindness,end up getting ignored & discarded from the blessings of them. If a child satisfies his/her parents at any cost then its ok,else...
Honestly speaking,after listening this kind of statement,I felt pathetic & pitiful.How can ability of a person can decide the love & importance of his/her parents.The love of parents are said to be most sacrificial, pious & pure,but after his such a great speech it seems that now parent's love have turned up materialistic,selfish & greedy.Now,it makes me believe that his thinking is something which is either personal experience,which he someday in his life had suffered & have gone through that dilemma,or may be his paradigms to love his children.Whatever it may be,this statement never satisfies my thought of assuming parent's love the most effective influencive selfless & eternal love. If this is the situation or thinking,then I must confess here wistfully,that real Love doesn't exists any more.
Parents may favour their one child amongst others for any situation, but loves equally to all & doing this,I think t is obvious.
-Fauzia Afreen