When it comes to advocating for a child, I am a firm believer in the power of mother's intuition.  Who could know better than mom (or dad) if a child is healthy or if something is not quite right?  So my first advice for parents is to trust your own feelings.  If you think something is going on with your child, it probably is.  Believe in yourself, and don't give up looking for the answer.  

In my experience, advocating for a child takes even more advanced planning than advocating for yourself.  You need access to accurate information 24 hours a day, seven days a week.  So it's important to figure out what your resources are before you need them.  Websites like EmpowHER.comcan provide quick access to medical information any time of the day or night.  But you may also need information when you don't have access to a computer.  So make sure you have a good book like Dr. Spock's classic Baby and Child Care.