Baptism not for non-Catholics

Here's a conversation between the Parish Priest and his catechist about Easter baptisms, (this was one of the questions asked by me in the English exam):

Catechist:  Father can you give baptism to non-Catholics also? Because last week two families approached me and asked about it.
Priest: No. We cannot give baptism to non-Catholics.  They can receive baptism only when they are converted to Christianity.
Catechist: Father, why only Catholic people receive baptism?
Priest: It should not be given to all.  Only those who are born Catholics are converted Catholics will receive baptism.  

The author of this conversation is one preparing for Priesthood, doing his second year of Philosophy!