"We teach many boys."
Translation:Multos pueros docemus.
No, they are different noun cases.
pueri is the nominative plural (can also be the vocative plural or genitive singular but won't explain those here) which is used as the subject of the sentence, the one doing the action. multi pueri docent -> many boys teach.
pueros is the accusative plural, often the direct object of the sentence; the one the action is being done to. multos pueros docent -> they teach many boys.