Me dio mucha ternura ver a mi sobrina dormida con su muñeco en brazos.

This is a very common Spanish pattern:

dar + noun of emotion/feeling + indirect object

So:

• me = to me
• dio = gave
• mucha ternura = a lot of tenderness / a strong feeling of tenderness

Very literally, Spanish says something like It gave me a lot of tenderness. In natural English, that becomes It made me feel very tender or I found it very touching / adorable.

This structure is used with lots of feelings:

• Me dio pena = It made me feel sad / I felt sorry
• Me dio miedo = It frightened me
• Me dio risa = It made me laugh
• Me dio vergüenza = It embarrassed me

So in your sentence, the thing that caused the feeling is ver a mi sobrina dormida con su muñeco en brazos.

Dio is the preterite of dar, and here it presents the feeling as a single reaction to a specific moment:

• Me dio mucha ternura ver... = Seeing ... gave me a strong feeling right then

If you used daba, it would sound more habitual, descriptive, or repeated:

• Me daba mucha ternura verla así = She used to make me feel very tender when I saw her like that / It would give me tenderness to see her like that

So dio fits a one-off emotional response to one scene.

Ternura is a noun meaning tenderness, affectionate softness, or the warm emotional feeling you get when something is sweet, innocent, or touching.

In sentences like this, English often translates it more naturally as:

• It was so sweet
• I found it adorable
• It was very touching
• It made me feel very tender

Spanish uses ternura a lot in emotional contexts where English might prefer sweet, adorable, or touching rather than the noun tenderness.

Related forms:

• tierno / tierna = tender, sweet, adorable
  
  • Qué tierna está tu sobrina = Your niece looks so sweet
• ternura = tenderness / sweetness

That is the personal a.

In Spanish, when the direct object is a specific person (or sometimes a pet or personified being), you usually use a before it:

• Veo a mi hermana
• Llamé a Juan
• Escuché a la profesora

So:

• ver a mi sobrina = to see my niece

You would not use this a with most non-person objects:

• Veo la casa
• Veo el coche

Even though mi sobrina is the object of ver, she is a specific person, so the personal a is required.

Both are possible, but they are not exactly the same.

dormida

This is the past participle used like an adjective. It describes her state:

• mi sobrina dormida = my niece, asleep

It focuses on how she looked: she was in a sleeping state.

durmiendo

This is the gerund. It emphasizes the ongoing action:

• mi sobrina durmiendo = my niece sleeping

That focuses more on the process or action.

In this sentence, dormida sounds very natural because the speaker is describing a tender visual image: the niece asleep, holding her toy.

So:

• ver a mi sobrina dormida = to see my niece asleep
• ver a mi sobrina durmiendo = to see my niece sleeping

The difference is small, but dormida often feels more pictorial and descriptive here.

Because it agrees with mi sobrina, which is feminine singular.

• sobrino dormido = nephew asleep
• sobrina dormida = niece asleep
• sobrinos dormidos = nephews asleep
• sobrinas dormidas = nieces asleep

Even though dormido/dormida comes from a verb, here it is functioning like an adjective, so it must agree in gender and number with the noun it describes.

It means she was with her doll/toy in her arms or holding her toy in her arms.

Breakdown:

• con = with
• su muñeco = her toy / doll / stuffed toy
• en brazos = in her arms

So the image is: the niece is asleep while holding the toy against herself.

This is a very natural Spanish expression.

Because en brazos is a very common idiomatic expression in Spanish.

It often means:

• in someone’s arms
• being held
• carried in arms
• held against the chest/arms

Examples:

• Llevaba al bebé en brazos = She was carrying the baby in her arms
• Se quedó dormido en mis brazos = He fell asleep in my arms

In your sentence, con su muñeco en brazos means she had the toy in her arms. Spanish often leaves the possessor implicit in expressions with body parts or fixed phrases when it is clear from context.

So en brazos sounds natural and idiomatic here.

Yes, su muñeco can be a little broader than English doll.

Depending on context, muñeco can mean:

• a doll
• a toy figure
• a cuddly toy / stuffed toy
• a little toy she sleeps with

In a sentence about a child asleep in bed, many English speakers would naturally say:

• her doll
• her teddy
• her stuffed toy
• her favourite toy

Also, su can technically mean his, her, its, your (formal), or their, but here context clearly points to the niece’s toy.

Because Spanish often uses an infinitive clause to express what caused the feeling.

So:

• Me dio mucha ternura ver a mi sobrina... = Seeing my niece ... made me feel very tender

The infinitive ver works like seeing in English.

This is very common after expressions of emotion or reaction:

• Me alegró verte = Seeing you made me happy
• Me sorprendió oír eso = Hearing that surprised me
• Me dio pena dejarlo solo = Leaving him alone made me feel sorry

So ver a mi sobrina dormida... is the event or scene that caused the emotion.

Yes, absolutely. That would be grammatical and natural.

The difference is mainly nuance:

• dormida = asleep, focusing on her state
• durmiendo = sleeping, focusing on the action

In this sentence, dormida often sounds slightly more natural if you are describing a still, sweet image. Durmiendo is also fine, just a little more dynamic.

So both work:

• Me dio mucha ternura ver a mi sobrina dormida...
• Me dio mucha ternura ver a mi sobrina durmiendo...

This word order is very normal in Spanish.

Spanish often puts the reaction first and then the cause after it:

• Me dio mucha ternura ver...
• Me dio pena escuchar eso
• Me dio rabia perder el tren

This structure is natural because it introduces:

1. the person affected
2. the feeling
3. the thing that caused it

You could rearrange parts in some contexts, but this version sounds very standard and smooth.

Yes. Spanish has several similar ways to express this kind of feeling, though each has its own tone.

Some close alternatives are:

• Me enterneció ver a mi sobrina dormida...
  = Seeing my niece asleep moved me / made me feel tender

• Me pareció muy tierno ver a mi sobrina dormida...
  = I found it very sweet to see my niece asleep...

• Qué ternura me dio verla dormida...
  = She looked so sweet asleep / Seeing her asleep gave me such a tender feeling

• Me dio muchísima ternura...
  = It gave me so much tenderness / I found it incredibly sweet

So me dio mucha ternura is a very natural, emotional, everyday way to say it.

It is general, widely understandable Spanish, and it sounds natural in Spain too.

A few notes for Spain:

• sobrina is completely standard
• muñeco is very normal
• dar ternura is also very natural in Spain

In some English translations for Spain-context Spanish, muñeco in a child’s bedroom scene might be understood as a cuddly toy, plush toy, or doll depending on context. But the Spanish itself is standard and not especially regional.