H.P.
All of the advice given so far sounds great. I frequently fly with my 4 1/2 year old and 1 year old (and have since they were 3 weeks old). Personally, I never take advantage of the early boarding they allow for small children. It keeps them cooped up longer. So I wait until the very last minute to get on, and usually ask the attendants at the gate to tell me when is the last possible second to board. Do bring extra changes of clothes for him and you...they love to poop out of their diapers when flying. Don't sweat it. You'll do fine! Good luck!