"A pony is a small horse."
Translation:Un poney est un petit cheval.
Petit precedes the noun in French. Petit cheval, petit enfant, petite voiture, petites chaussures, etc...
The way I was taught to remember this in school was using the mnemonic BAGS: beauty, age, goodness, size. Adjectives referring to one of those properties precede the noun. It's probably not perfect, but it works well!