@Ted41 - I have a friend who works with autistic children, which isn't exactly the same as a child with a developmental problem. However, the parents act a lot like what you were describing. They're often really stressed out, and sometimes take their feelings out on my friend. So you have to have a really thick skin to work early intervention specialist jobs, I'm sure.
That being said, I bet the job is very rewarding too. Imagine if you could help a child overcome a developmental problem, and go on to develop normally for the rest of their life? That has to be a great feeling.