Having a favourite child is Haram in islam

 Allah creates us , mother is just a media to conceive and given birth to. The colour of the skin to the the knowledge, has given by Allah. So if you are choosing one child over your other children that's a sin. 

No matter how many kids you have all your kids have one father and a mother. They have emotions, they have desires, they need love , they need protection. In the time when they don't get those they decides to find it from somewhere else and falling in to trouble.

You may love your first born because you created him /her with love . And you do everything for that particular child without missing from branded cloths to everything. 

When your second child is born your were getting so busy and have no time to care or love even your self.

When you get busy and feeding , changing diapers , sleeping with 2nd child , your elder one thinks that you don't care for them anymore.

So it's our duty as parents to keep them mentally healthy by ask their help when feeding , Changing diapers, and can ask them to kiss often .

So loving one kid for they are obedient and hating another kid for being naughty is prohibited in Islam . They need time to correct them self . Punishing a small kid for their mistake is the foolish thing I ever see. Because they are just begginers and learning everything.

We must teach them what is right and what is wrong. It will take time but they will learn slowly. Look at their eyes and talk to them . 

Look in to their eyes and tell them I love you ! 

You are my champion, you are my pride. Their everything is you . They will show their anger ,love and everything to you.

Keep it in mind , they will remember everything you do for them , they will treat you as you treat them . So be careful when raising kids