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: 
One approach to this I encountered in the novels "A Series of Unforunate Events" by Lemony Snicket (which were definitely intended mainly for a teenage audience) is to use big words as an example to **TEACH** them.

For example, the second-to-last book is called "The Penultimate Peril". In the beginning of the book, the author (who is himself a character who narrates the story) explains what the word "penultimate" means.

This was sort of a trope that would reappear in the series, but there could other ways to explain what the words means without taking someone out of the story
So keep in mind that much of the English Language Literature on the market (especially modern written novels) is written at an 8th grade (US) reading level, which corresponds to about 13-14 years old. Most English courses beyond 8th grade will read some selections of English Language Classical Literature that may be centuries old and use archaic word usage and meaning that is no longer relevant (Shakespeare is quite popular as the Bard is known for clever puns that are funny if you know the slang of his time... most of which are playing off of references to genitalia. I also recall reading "Bartleby the Scrivner" by Herman Melville (more difficult than Shakespeare) and the "Rhyme of the Ancient Mariner" and "Beowulf" (mercifully not in the original old English, which is so different from the modern language that it requires a translator) and "The Tyger" by William Blake, which has some rhyming pairs that only rhyme if you use different pronunciations then the modern sound of the word (for example, there is a part in the poem where "Eye" is rhymed with "Symmetry" which did rhyme at the time Blake originally wrote the poem, but doesn't today. English is weird).

Using big word in works meant for children isn't uncommon, and in fact, many a Disney film (especially in the animated cannon) used some advanced words for a kids movie (my middle school vocabulary textbook actually made an effort to look at famous pop culture kids films for words to use in each chapter). Check some Disney films of old, and even those of today and there will be a a word or two that kids may not hear every day, but will understand with age. It's actually why adults still will watch the films as it's fun seeing the stuff they missed. Just some examples, but the Latin Chanting in "Hunchback of Notre Dame" is actually pretty important and requires not only an understanding of translation, but it's place in the Catholic Church's mass and sacraments, specifically, the Sacrament of Reconciliation (Confession) and depicts one of the aspects of the Sacrament that you don't see often on TV (namely, the confession booth is notably absent but the communal aspect of the rite is depicted in part (typically, tv shows the reverse)... and the reason for this is rather significant in understanding the Villain. A more recent example, Zootopia, makes a pretty blatant reference to "Breaking Bad" which no child will understand, and Frozen Opens with a depiction of Ice Harvesting, which was last a thing when my Grandfather was a boy.

There's also the general rule that children's literature is allowed to get away with more then what would be in the movies or tv because the depiction of violence and mature situations is all within one's own imagination rather than on a screen and thus the kids will "see" what they are comfortable with imagining.