yubi wo kegasita node, haha ga bansoukou wo hatte kuremasita.

Because 指 is the thing that got injured, so it is treated as the direct object of けがした.

Japanese often does this with body parts:

• 指をけがした = injured my finger
• 足をけがした = injured my leg/foot
• 頭を打った = hit my head

In English, we usually say I hurt my finger, where my finger is also the thing affected, so the idea is similar.

They are closely related, but they are used a little differently.

• けがをした = had an injury / got hurt
• 指をけがした = injured a finger

When you name the body part, Japanese commonly says:

• 指をけがした
• ひざをけがした

When you do not name the body part, けがをした is very common.

So in this sentence, 指をけがした is the natural way to say hurt my finger.

Both can mean because, but ので usually sounds a bit softer, more explanatory, and less direct than から.

• 指をけがしたので、母が絆創膏を貼ってくれました。
  • Because I hurt my finger, my mother put a bandage on it for me.

If you used から, it would still be correct:

• 指をけがしたから、母が絆創膏を貼ってくれました。

But ので often feels a little more gentle and descriptive, which fits well here.

Using が here focuses on who did the action.

• 母が絆創膏を貼ってくれました = My mother is the one who put the bandage on me.

If you used は, it would make mother the topic, and it could sound more contrastive depending on context:

• 母は絆創膏を貼ってくれました = As for my mother, she put a bandage on it for me.

So が is a very natural choice when introducing the person who performed the action.

This is 貼る in the て-form plus くれる.

• 貼る = to stick on, attach, put on
• 〜てくれる = do something for me / for someone in my in-group

So:

• 貼ってくれました = put it on for me

This adds a sense that the action was done as a favor or in a helpful way. It is not just a neutral statement that she applied a bandage. It shows that the speaker benefited from the action.

Compare:

• 母が絆創膏を貼りました = My mother put on a bandage.
  Neutral statement.

• 母が絆創膏を貼ってくれました = My mother kindly put a bandage on for me.
  The speaker receives the benefit.

Because the action is already completed.

The sentence describes two past events:

1. the finger got injured
2. the mother put a bandage on it

So both are in the past:

• けがした
• 貼ってくれました

If this were happening right now, the tense would be different.

In Japanese, 母 usually refers to my mother when speaking to someone else.

This is different from お母さん, which is often used:

• when talking directly to your mother
• when referring to someone else’s mother
• sometimes casually for your own mother in conversation, depending on context

So 母が strongly suggests my mother.

Japanese often leaves that unstated if it is obvious from context.

Here, the most natural interpretation is that it was the speaker's finger, because:

• the sentence has no other likely owner of the finger
• 貼ってくれました shows the speaker received the benefit
• the whole sentence naturally reads as I hurt my finger, so my mother put a bandage on it for me

Japanese frequently omits words like I, my, and me when they can be understood.

Because 貼る is the normal verb for sticking something onto a surface.

A bandage like 絆創膏 is adhesive, so Japanese says:

• 絆創膏を貼る = put on a bandage

Other common combinations are:

• シールを貼る = stick on a sticker
• 切手を貼る = stick on a stamp

So 貼ってくれました is exactly the verb you would expect with 絆創膏.

The main readings are:

• 指 = ゆび
• 母 = はは
• 絆創膏 = ばんそうこう
• 貼って = はって

So the full sentence is read:

ゆび を けがした ので、はは が ばんそうこう を はって くれました。

Because Japanese often omits information that can be understood from context.

In English, you would usually say something like:

• I hurt my finger, so my mother put a bandage on it for me.

In Japanese, the listener can usually infer:

• who got hurt
• whose mother it is
• who received the favor

This omission is extremely common and natural in Japanese.

Yes. 絆創膏 is the standard word for an adhesive bandage, but in everyday speech many people also say:

• バンドエイド

That is originally a brand name, but it is often used like a general word, similar to how some brand names are used in English.

So both of these are natural:

• 絆創膏を貼ってくれました
• バンドエイドを貼ってくれました