Breakdown of Дети любят смотреть, как вертолёты взлетают.
любить
to love, to like
как
how
смотреть
to watch / to look at / make sure (in a warning)
дети
children
Questions & Answers about Дети любят смотреть, как вертолёты взлетают.
How does the prefix вз- change the meaning of the verb here?
The prefix вз- (or вс- before voiceless consonants) adds the meaning of upward movement. Combined with летать (to fly), взлетать literally means 'to fly up,' which is the standard Russian way to say 'to take off' for aircraft or birds.
Why is взлетают in the imperfective aspect here?
Because the sentence describes a general, repeated action. The children love watching helicopters take off in general, not just one specific helicopter completing a single takeoff. The perfective form would be взлетят, but that doesn't fit a regular habit.
Why do we use the imperfective infinitive смотреть instead of the perfective посмотреть?
After verbs expressing a general preference or habit, like любить (to love) or нравиться (to like), Russian almost always requires the imperfective infinitive. They love the ongoing process of watching, not just a one-time completed action.
Why does the sentence use как instead of just saying the Russian equivalent of 'watch helicopters take off'?
Unlike English, where you can say 'watch helicopters take off' (verb + object + bare verb), Russian requires a subordinate clause for this. When observing an action as it happens, Russian uses смотреть, как or видеть, как (to watch how / to see how) followed by a fully conjugated verb.