I chose to go a little bit of a different route, i think almost everyone will get the McLevin hit on superbad (thats a classic movie) so I focused more on what I would think the attributes of your son would be. The font is done very bold and bright, How I would picture your son being, the 47 is noticably smaller because despite the down syndrome, i feel that it will be very small in comparision to what he will offer the world over his lifetime. The tiger is a symbol of strength, being drawn, it gives a nice "childlike feel" to the logo, lastly behind the tigher is a full halo, because your son is a gift, a little angel from God if you will. I Hope you like it, it was by far the most satisfying design that I have done in a long time.