QUESTION: Given the sentence "Four kids are jumping on a trampoline." is it true that "Kids are jumping on a trampoline."?

Let's solve it slowly: Four kids are jumping on a trampoline and it's the same as phrasing them as kids jumping on a trampoline.
The answer is yes.

QUESTION: Premise: "Two young people trek through a green wooded area."
Hypothesis: "A cat is yawning."
Do we know that the hypothesis entailed by the premise?

Let's solve it slowly: Two young people are not a cat. Trek is not yawning.
The answer is no.

QUESTION: Premise: "Two men in the foreground are looking at one another while a man in the background in bright blue is walking."
Hypothesis: "Two men are watching as their brother gets closer to them."
Do we know that the hypothesis entailed by the premise?

Let's solve it slowly:
A man is walking does not imply a brother that gets closer.
The answer is it is not possible to tell.