The official artistic reason for the halos was to distinguish otherwise normal looking people from the more "mundane" people around them. After all, without a halo, Baby Jeebus is just another crying baby, and how else is your audience (or the Pope) going to know the difference between him and the 5 others you've painted in the picture?
It got started in the Byzantine mosaic murals to separate the Emperor and his family (the chosen agents of G-d) from other members of the court/peasants on the street. It then spread to iconography, and then to the wider artistic world as a means of representing supposed "holy" personages. If you'll notice, there are no depictions of saints/angels/Jeebus with halos before about 500-750 C.E., even though the people being depicted had been revered and sanctified for centuries already.
And should it be that we shall never meet again,
Know that I will always keep you in my heart,
And I will search for you in that time beyond time
Until we do meet again, and you will know
That love and family are the miracles of the world.