"He has small elephants."
Translation:Il a de petits éléphants.
When there is an adjective before a plural noun you use "de" instead of "des". If you are saying "he has elephants" you would say "il a des elephants" but if "he has small elephants", it's "il a de petits elephants." Another example "elle a de grands yeux bleus" - "she has big blue eyes."
And "de" is necessary! ....as i previously had the same question.
"de" (variation of "des" because of the adjective that follows) is a plural indefinite article (or determiner) that means "some".
Most adjectives go after the noun in French, but there are certain very common adjectives that precede the noun. To help you remember, the acronym is BANGS (or sometimes BAGS if number isn't included).
Beauty - belle/joli
Age - jeune/vieux
Number - un, deux, trois
Goodness - bon/mauvais
Size - petit/large
Of course there are more words that fit into each of these categories, and then there are a few exceptions too. This is a general rule and you will be right most of the time if you follow it.
Il a de petits éléphants is the correct word order.
Here's a link: https://www.lawlessfrench.com/grammar/adjectives/
Ugliness which describes attractiveness is an exception: moche/laid go after the noun.