In A Midsummer Night's Dream, why are Oberon and Titania fighting over an Indian Boy?

Titania and Oberon quarrel over the changeling boy because they both want the boy for very different reasons. 

Puck reveals to us in Act I: 

Puck: And jealous Oberon would have the child. Knight of his train to trace the forests wild.

Oberon wants the boy to be basically his henchman. 

Meanwhile, Titania has motherly love for the changeling boy because one of the women who worship her died in childbirth and gave the boy to Titania. 

A more subtle interpretation of the text suggests that Oberon is also simply jealous of all the attention and love Titania pours out for the changeling boy.