otouto ha omosiroi sutanpu wo mitukeru to, kazoku no guruupu ni sugu okuru.

は marks 弟 as the topic of the sentence.

So 弟は means something like as for my younger brother or my younger brother as the topic we are talking about.

It does not simply mean subject in every situation, but in this sentence, 弟 is also the doer of the actions:

• 見つける = finds
• 送る = sends

A learner might expect が, but は is very natural when introducing what someone generally does or describing a habitual action.

In Japanese, adjectives normally come before the noun they describe.

So:

• 面白いスタンプ = an interesting/funny stamp

This is just like:

• 大きい犬 = a big dog
• 新しい本 = a new book

Here 面白い directly modifies スタンプ.

Probably not a postage stamp.

In modern Japanese, スタンプ often means a chat sticker or messaging app stamp, especially on apps like LINE.

So in this sentence, it most likely means:

• a funny sticker/image used in messages

That makes the second half very natural:

• he finds a funny sticker
• then sends it to the family group

を marks the direct object of the verb.

Here, the object of 見つける is 面白いスタンプ:

• 面白いスタンプを見つける = find a funny stamp

So を tells you what is being found.

This is a very common question.

In the pattern verb dictionary form + と, と means something like:

• when
• whenever
• if/once in an automatic or regular sense

So:

• 見つけると、送る means
• when he finds one, he sends it
• whenever he finds one, he immediately sends it

This pattern often describes a habitual action, general tendency, or an automatic result.

If you used 見つけたと, that would not work in the same way here.

Here と is a conditional/temporal marker.

It connects:

• 面白いスタンプを見つける = when he finds a funny stamp with
• 家族のグループにすぐ送る = he immediately sends it to the family group

So the whole structure is:

• X と、Y
• When/whenever X happens, Y happens

Important nuance: ～と often sounds like the second action follows naturally, regularly, or almost automatically.

So this sentence feels like a general habit:

• Whenever my younger brother finds a funny sticker, he immediately sends it to the family group.

The object is omitted because it is understood from context.

Earlier in the sentence, we already have:

• 面白いスタンプを見つける = find a funny stamp

So when the sentence continues with:

• 家族のグループにすぐ送る = immediately sends it to the family group

the listener naturally understands that it means the stamp/sticker he found.

Japanese often leaves out words that are obvious from context.

If you said everything explicitly, it might look like:

• 面白いスタンプを見つけると、それを家族のグループにすぐ送る。

But それを is unnecessary here.

に marks the destination or target of 送る.

So:

• グループに送る = send to the group

With verbs like 送る, に often shows:

• the person you send something to
• the place/group/chat you send something to

Here:

• 家族のグループに = to the family group

Literally, it means family’s group or group of the family.

The particle の connects nouns, and in this sentence it works like:

• family group
• the family chat/group

So:

• 家族 = family
• 家族のグループ = the family group / family chat group

In natural English, this would often be translated as:

• the family group chat even though chat is not explicitly written.

すぐ means:

• immediately
• right away
• soon

Here it modifies 送る:

• すぐ送る = send immediately

Its position is very natural:

• 家族のグループにすぐ送る

Japanese adverbs like すぐ are often placed before the verb they modify.

It most naturally sounds like a habit or repeated behavior.

That feeling comes from:

• 弟は as a topic
• dictionary-form verbs
• ～と meaning whenever/when
• the overall structure describing what he tends to do

So it sounds like:

• Whenever my younger brother finds a funny sticker, he immediately sends it to the family group.

If you wanted a one-time past event, Japanese would usually be phrased differently.

Yes. 面白い can mean both interesting and funny/amusing.

In this sentence, because the noun is スタンプ and the action is sending it to a family group, funny or amusing is probably the more natural sense.

So:

• 面白いスタンプ = a funny sticker / an amusing stamp

But the exact nuance depends on context.

Japanese non-past forms are used not only for the future, but also for:

• habitual actions
• general truths
• repeated behavior

So here:

• 見つける = finds / whenever he finds
• 送る = sends

This does not necessarily mean future time only. It describes what he generally does.

That is why a natural English translation often uses the present simple:

• Whenever he finds a funny sticker, he immediately sends it to the family group.