Mon petit frère efface un mot avec sa gomme, puis le réécrit avec un crayon plus foncé.

In French, the possessive adjective agrees with the gender and number of the noun possessed, not with the possessor.

• frère is a masculine singular noun → you must use mon.
• ma is used only before feminine singular nouns (e.g. ma sœur).

So you say:

• mon frère, mon petit frère
• ma sœur, ma petite sœur

In French, many common adjectives go before the noun. Petit is one of them.

Typical adjectives that usually come before the noun include:
beau, grand, petit, jeune, vieux, bon, mauvais, gros, long, nouveau, etc.

So:

• mon petit frère = my little brother
  not mon frère petit (which would sound strange in this context).

Efface is the present tense, 3rd person singular of effacer.

French usually uses the simple present (il efface) where English might use the present progressive (“he is erasing”).

So:

• Mon petit frère efface un mot…
  = “My little brother is erasing a word…”

You generally don’t say est en train d’effacer unless you really want to emphasize the ongoing process (“is in the middle of erasing”).

Un mot uses the indefinite article (a word), meaning “some word / one word, not specified which one”.

If you said le mot, you would be talking about a specific word already known from the context, like:

• Il efface le mot qu’il a mal écrit.
  He erases the word that he wrote badly.

Here the context is just “a word” in general, so un mot is natural.

In French, when talking about parts of someone’s body or personal belongings in obvious contexts, you often use the possessive adjective:

• sa gomme = his eraser (literally “his/her rubber”)
• mon stylo = my pen
• ses lunettes = his/her glasses

La gomme would be more like “the eraser” in a neutral or generic sense, not clearly tied to him.

Since it’s his own eraser, sa gomme is the most natural phrase.

The choice between son / sa / ses depends on the gender and number of the noun, not on the first letter:

• gomme is feminine singular → sa gomme
• son is used with masculine singular nouns (e.g. son frère) and also with feminine nouns starting with a vowel sound (e.g. son amie).

So we have:

• sa gomme (fem. sing.)
• son crayon (masc. sing.)
• ses crayons (plural)

In this sentence:

• puis = then, after that.

It’s a neutral, common way to show sequence.

Differences:

• puis: simple, neutral “then”.
• et puis: often a bit more conversational, can feel like “and then…”.
• ensuite: also “then/next/afterwards”, with a slight nuance of next step in a sequence.

Here, puis is perfectly natural:
…efface un mot avec sa gomme, puis le réécrit…
= “…erases a word with his eraser, then rewrites it…”

Le is a direct object pronoun meaning “it” (masculine singular).

It replaces un mot:

• Mon petit frère efface un mot… puis il réécrit le mot…
  → To avoid repeating le mot, French replaces it with le:
• …puis le réécrit… = “…then rewrites it…”

So le = un mot (a word).

In French, object pronouns normally come before the conjugated verb:

• Il le lit. = He reads it.
• Je la vois. = I see her/it.
• Nous les avons vus. = We saw them.

So:

• puis le réécrit = “then rewrites it”
  not puis réécrit le.

Réécrit is the 3rd person singular present of réécrire:
réécrire = to rewrite

• il réécrit = he rewrites

Spelling:

• The verb is built from ré- (again) + écrire (to write).
• When joined, you get réécrire with two é in a row.
• In the present tense, il réécrit keeps both é: ré + écrit → réécrit.

Pronunciation: the double é gives essentially a single long “ay” sound, not two clearly separated syllables. It sounds close to [ʁeekʁi].

The full idea is indeed:

• avec un crayon plus foncé que l’autre
  = “with a pencil that is darker than the other one.”

But French often leaves out the second part when it’s obvious. Here, context makes it clear he uses a darker pencil than the first one he wrote with, so:

• avec un crayon plus foncé
  is understood as “with a darker pencil (than before / than the previous one).”

Foncé means “dark” when talking about colors (dark blue, dark red, etc.).

Adjectives must agree with the noun:

• un crayon is masculine singular → un crayon foncé.
• If the noun were feminine singular, you’d say foncée:
  • une robe foncée (a dark dress)
• For plurals:
  • des crayons foncés (dark pencils)
  • des robes foncées (dark dresses)

So here: un crayon plus foncé is correct because crayon is masculine.

French often uses the present tense to:

1. Describe a current, concrete action (what your brother is doing right now), or
2. Tell a simple story or example in a vivid way (the “narrative present”).

So:

• Mon petit frère efface un mot… puis le réécrit…
  can be:
  • describing what he is literally doing now, or
  • giving a generic example of what he habitually does.

If you wanted a past description, you might say:

• Mon petit frère a effacé un mot… puis l’a réécrit…
  (passé composé: “erased… then rewrote it”).