By logic, it's technically impossible for the parents to provide the same attention to all of their children. The real question, how prominent is this favoritism?
Not all children are the same, some are academically successful, others triumph in sports, etc. Say, three children in a family have marginally different academic capabilities and the family can only afford university for one. The most able of the children could easily ace university.
Now in this case, one logical solution would be to send the most able child to the university. Could this be viewed as favoritism? Surely, because it technically is. Would it be a more logical solution for the family to pay the same further education to all three children? That'd prevent the most academically able from acing a university it could easily ace.
Hard question, but I think it all revolves around the amount of favoritism and the reasoning behind it. But yes, favoritism definitely occurs in most families.