Chúng ta phải hủy buổi dã ngoại.

Chúng ta means we including the person you are speaking to.
Chúng tôi means we excluding the person you are speaking to.

So in Chúng ta phải hủy buổi dã ngoại, the speaker is including the listener: we all have to cancel the picnic.

Compare:

• Chúng ta phải đi ngay. = We have to go now. (including you)
• Chúng tôi phải đi ngay. = We have to go now. (not including you)

This is a very important distinction in Vietnamese and often surprises English speakers, since English we does not make this difference.

Here, phải means must, have to, or need to.

So:

• phải hủy = must cancel / have to cancel

It expresses obligation or necessity.

Examples:

• Tôi phải làm việc. = I have to work.
• Bạn phải cẩn thận. = You must be careful.

In this sentence, phải shows that canceling the picnic is necessary, not optional.

Yes. Hủy is a very common verb meaning to cancel.

Examples:

• hủy cuộc họp = cancel the meeting
• hủy vé = cancel the ticket / booking
• hủy chuyến đi = cancel the trip

In hủy buổi dã ngoại, it means canceling the picnic event.

A common related form is hủy bỏ, which also means cancel or call off. In many situations, hủy and hủy bỏ are both acceptable, though hủy is shorter and very common in everyday use.

Buổi is a noun/classifier-like word used for an occasion, session, or event.

So:

• buổi dã ngoại = the picnic outing / the picnic event

Vietnamese often uses words like this where English would not. You can think of buổi as helping package the activity into a specific event.

Other examples:

• buổi học = class session
• buổi họp = meeting session / meeting
• buổi sáng = morning

In this sentence, buổi dã ngoại sounds natural because it refers to the picnic as a planned occasion.

Dã ngoại means outing, excursion, or picnic, especially an outdoor leisure trip.

So buổi dã ngoại is a picnic or outdoor outing.

Depending on context, it may suggest:

• a school outing
• a company outing
• a picnic with friends or family

If the meaning shown to the learner is picnic, that is a very natural translation here.

The sentence follows a very common Vietnamese pattern:

Subject + phải + verb + object

Here:

• Chúng ta = subject
• phải = must / have to
• hủy = verb
• buổi dã ngoại = object

So:

Chúng ta / phải / hủy / buổi dã ngoại.
= We / have to / cancel / the picnic.

This order is straightforward and often maps quite closely to English.

You may hear shorter phrases in casual speech, but Chúng ta phải hủy buổi dã ngoại is more complete and natural if you mean the picnic event.

Without buổi, dã ngoại sounds more like the activity in general rather than a specific outing.
Using buổi makes it clearer that you are canceling a particular planned occasion.

So for learners, buổi dã ngoại is the safer and more natural choice.

No. Vietnamese does not have an article system like English a/an/the.

So buổi dã ngoại can mean:

• a picnic
• the picnic

The exact meaning depends on context.

In a real situation, listeners would understand whether this is a specific picnic already known to everyone. English usually has to choose the picnic, but Vietnamese often leaves that unstated.

You could replace phải with a softer expression, such as:

• nên = should
• có lẽ nên = maybe should

Examples:

• Chúng ta nên hủy buổi dã ngoại. = We should cancel the picnic.
• Chúng ta có lẽ nên hủy buổi dã ngoại. = We should maybe cancel the picnic.

So phải is stronger than nên.

You can add không before phải if you mean do not have to:

• Chúng ta không phải hủy buổi dã ngoại. = We do not have to cancel the picnic.

If you mean must not cancel, that is different. You could say:

• Chúng ta không được hủy buổi dã ngoại. = We must not / are not allowed to cancel the picnic.

This is a useful distinction:

• không phải = do not have to
• không được = must not / not allowed to

A rough pronunciation guide for English speakers is:

• Chúng ta ≈ choong ta
• phải ≈ somewhat like figh with a falling-rising tone
• hủy ≈ roughly hwee with a hỏi tone
• buổi ≈ roughly boo-ee with a falling-rising tone
• dã ngoại ≈ roughly yah ngo-eye with tones

A few important notes:

• ph in Vietnamese is pronounced like English f
• d in southern Vietnamese is often like English y, while in northern Vietnamese it is more like z
• tones matter a lot, especially in phải, hủy, buổi, and dã

If you are learning pronunciation, it is best to listen to native audio, because English-style approximations can only go so far.

Yes, absolutely. It sounds natural and standard.

It would fit situations like:

• bad weather
• someone is sick
• not enough people can come
• transportation problems
• a schedule change

For example:

• Trời mưa rồi. Chúng ta phải hủy buổi dã ngoại.
  = It’s raining. We have to cancel the picnic.

So this is a very usable real-life sentence.