La niñera dice que la pequeña ya empieza a gatear por el pasillo cuando nadie la mira.

After verbs like decir, Spanish normally uses que to introduce what someone says, thinks, knows, etc.

So:

• dice que... = says that...

In English, that is often optional, but in Spanish que is usually kept.

Examples:

• Dice que viene mañana. = She says that she’s coming tomorrow.
• Creo que tienes razón. = I think that you’re right.

La pequeña literally means the little one or the little girl. It is a very natural way to refer to a child, especially when the speaker wants to sound affectionate or simply focus on her being small.

So:

• la niña = the girl
• la pequeña = the little girl / the little one

Both are possible, but la pequeña often sounds a bit more descriptive or tender.

Here ya means already.

It suggests that this action has begun sooner than expected, or that the child has reached that stage now.

So ya empieza a gatear gives the idea of:

• she’s already starting to crawl
• she has now started to crawl

Depending on context, ya can also mean now or by now, but already is the clearest meaning here.

Because empezar is followed by a when another verb comes after it.

Pattern:

• empezar a + infinitive

So:

• empieza a gatear = starts to crawl
• empezó a hablar = started to speak
• empiezan a correr = they start running

This is just the standard construction in Spanish.

Gatear means to crawl, especially the way a baby crawls on hands and knees.

It is the normal verb for that developmental stage.

Related idea:

• caminar = to walk
• andar = to walk / go around
• gatear = to crawl

So this sentence is specifically about the child not walking yet, but moving around by crawling.

Por el pasillo means something like along the hallway, down the hallway, or through the hallway area.

Por often expresses movement through or along a place.

Compare:

• Va por la calle. = He’s going along/down the street.
• Corre por el parque. = She runs around/in the park.
• Gatea por el pasillo. = She crawls along/down the hallway.

If you said en el pasillo, that would focus more on location: in the hallway.
But por el pasillo emphasizes movement within that space.

Because nadie is grammatically singular.

So Spanish uses a singular verb:

• nadie mira
• not nadie miran

Even though nadie refers to no person / nobody, the verb stays singular, just like English nobody looks rather than nobody look.

The la refers to la pequeña.

It is a direct object pronoun, meaning her.

So:

• nadie la mira = nobody looks at her

In Spanish, object pronouns usually go before a conjugated verb:

• la mira = looks at her
• lo conoce = knows him
• las ve = sees them

Spanish does not say mira la in this kind of structure.

Because mirar usually means to look at or to watch, while ver means to see.

Here the idea is that nobody is actively watching the child.

So:

• nadie la mira = nobody is looking at her / watching her
• nadie la ve = nobody sees her

Both are possible in some contexts, but mirar fits better when the meaning is watching or paying attention visually.

The present tense is being used to describe a current or general situation.

This sentence sounds like the nanny is reporting something that is true now, or something that happens habitually:

• The nanny says
• the little girl is already starting
• when nobody looks at her

Spanish often uses the present for things that are currently happening or regularly happen, even where English might sometimes choose a slightly different form depending on context.

Because this sentence describes a repeated or general situation:

• when nobody looks at her
• whenever nobody is watching her

With cuando, Spanish uses the indicative when talking about something habitual, repeated, or considered real.

So:

• cuando nadie la mira = when/whenever nobody is looking at her

If it referred to a future, not-yet-real event, Spanish would often use the subjunctive instead:

• cuando nadie la mire = when nobody looks at her / when nobody is watching her, in a future sense

But in your sentence, it is a general pattern, so mira is correct.

It can mean either babysitter or nanny, depending on context.

In Spanish, niñera is a woman who takes care of children. English often separates:

• babysitter = usually occasional childcare
• nanny = more regular or professional childcare

Spanish does not always make that distinction clearly with a different word, so niñera can cover both ideas. The context decides which English word fits best.