I'm a middle child! I will celebrate today by staying under the radar, being anonymous, never standing out, and giving up my place in all aspects of society!
Why? Because I am a middle child! The one no one notices. The one everyone forgets. The one that inspired the movie "Home Alone..." 
I'm also a middle child which happened to be compounded with the fact I have an older brother and a younger sister.
As a male, the older sibling got way more freedoms and assistance earlier in life.
As a female, the younger sibling was "the baby" and "the only girl". So, she was pampered, protected and given much more support than the boys.
Flip-side to the story is that a middle child ordinarily learns to be more independent, self sufficient, and more likely to excel in their studies and employment. They are less dependent on others to teach them things, and are more capable of using available resources to learn from instead.
Once the older and younger children are on their own, they have a big adjustment to deal with, now that they don't have mommy or daddy to shelter them. Not as big a change for me when I I left home.