Question: I was writing the other day and I used the word "ubiquitous". 

While I don't think "ubiquitous" is the most egregious example of "Using Big Words To Sound Intelligent", and would be perfectly acceptable in most novels, it's just, my novel's demographic would be young teenagers, and I definitely did not know what ubiquitous meant when I was a young teenager.

Personally, when I come across an unknown word in a book, I have to take a minute to research what that word means, taking me away from the book.

On the other hand though, this could be seen as a teaching moment where I can teach young readers the meaning of new words

Answer: 
Don't use a big word when a singularly unloquacious and diminutive linguistic expression will satisfactorily accomplish the contemporary necessity.
No.

Use the words that you want/need to use.

Kids have NO idea what is or is not a big word. Kids are a blank slate. Every word is big to them. So no word is big to them.

This is why there are plenty of 4 year olds who can rattle off the scientific names of dozens of dinosaurs.

Big words are not a problem for kids. To you it is a big word. To kids it is just a word.

Use the words you want to use. And use them appropriately.