DO be polite, be thoughtful, understand that even though this situation is taking control of your life that their job is full of people JUST LIKE YOU. These folks - from nurses to doctors - have spent YEARS OF THEIR LIVES and THOUSANDS OF DOLLARS to be able to do what they do.
This does not mean, however, that they (or any of them) know EVERYTHING. I've often heard doctors say things that I thought were crazy and wrong. When this happens to you (and it will) just start - politely - asking questions.
Some doctors have great bedside manners, some (like a certain brilliant cardiac surgeon in Texas) have the bedside manner of a rattle snake. Be thankful for the ones that are nice and caring and hold strong with those that aren't.
Some nurses will let you help care for your child - if you can stomach what's going on - ask to help. Some will not. This is not because they think you are incompetent - they have a lot of regulations and they know the procedures better than you do.
During our experiences I've helped do spinal tap, suction airways, aspirating wounds and change bandages. In the ICU they often do smaller "procedures" You probably won't be able to help with those... and you probably don't want to. Just ask that your child be given painkillers (if necessary) and has an advocate telling them what is going on (if they are awake).