Learn Spanish (Latin America): Terminaron reventando todos los globos.

In Spanish, you use the verb terminar (to finish/end) followed directly by a gerund (a verb ending in -ando or -iendo) to express that someone "ended up" doing something. Here, terminaron (they finished) + reventando (bursting) combines to mean the final, perhaps unplanned, result was that they burst the balloons.

Could I use acabaron instead of terminaron in this sentence?

Yes! The verbs terminar and acabar are completely interchangeable in this specific structure. Saying acabaron reventando todos los globos means the exact same thing and is just as common in everyday speech.

Why don't we need a preposition like de after terminaron?

It depends on what you want to say! If you add de and use the infinitive (terminaron de reventar todos los globos), it means "they finished bursting all the balloons" (they completed the task). By dropping the preposition and using the gerund (reventando), the meaning changes to "they ended up bursting" (a resolution or unexpected outcome).

The verb is reventar (to burst). Since it's a stem-changing verb, why isn't it revientando?