The great St. Thomas tell us that the moment a child is born God calls one of His glorious Angels and gives the new born baby into his special care. It is not when the soul is created  (at the moment of conception) and united to our bodies, for then the child is still one with its mother and protected by the mother's Guardian Angel, but when we are born into the world that our Angel begins his care of us, even before Baptism.

Every person, whether pagan, heretic or Catholic has a Guardian Angel. Though one Angel would be powerful enough to take perfect care of a thousand souls, yet God in His infinite goodness has given to each one of us a special Angel, an Angel who is all our own, whose great duty from then on will be to watch over us day and night, asleep or awake, alone or in the midst of company, in our homes, in the street, working or resting, everywhere, every moment of our lives, in joys and in troubles. he never abandons us for a single instant; he sees our every movement; he is ever at our sides.

It seems at first sight incredible that God gives each of us poor mortals a glorious Prince of Heaven to guide and guard us all the days of our life, who is with us night and day, who devotes all his time, all his care, all his unceasing vigilance to secure our happiness. But in pure truth, it is only one of the many immense proofs of love which our dear Lord has given us.

What personal favors has not God Himself already done us. Did He not create us with His own hands, making us to His own image and likeness? Did He not raise us up to the highest possible destiny that He could give, namely to be with Him as His children forever in Heaven, seated on thrones in His presence, enjoying infinite joys for all eternity? Is He not our Father?

Did He not suffer and die for each one of us? Does He not come into our souls, uniting Himself to us most intimately, countless times in Holy Communion? Does He not watch over us every moment so that not a single hair falls from our heads without His permission? But what is really amazing is that we do not appreciate, do not understand as we should this divine favor; that we do not prize and love and seek to know better this glorious Angel who is so good to us. Our neglect of our dear Angel is appalling.

Taken from the book "All about the Angels" by Father Paul O'Sullivan, O.P.E.D.M.