Desde niño he sentido curiosidad por el universo y por las estrellas.

In desde niño, niño is being used almost like an adjective to describe me (the speaker), not as a specific child with an article.

• desde niño literally = “since (I was) a child”
• There is an implied yo era or siendo:
  • Desde niño (yo era / yo he sido / yo estoy) curioso…

You could say desde la niñez (“since childhood”), but that’s a different structure:

• Desde niño he sentido curiosidad… = Since I was a child, I have felt curiosity…
• Desde la niñez he sentido curiosidad… = Since (my) childhood, I have felt curiosity…

Both are correct; desde niño is a very natural, common pattern in Spanish.

Yes. Niño / niña agrees with the gender of the person speaking.

• A man: Desde niño he sentido curiosidad por el universo…
• A woman: Desde niña he sentido curiosidad por el universo…

Same idea with other similar expressions:

• Desde pequeño / pequeña
• Desde chico / chica (very common in Latin America)

Yes. Desde + a point in time usually implies “from that time up to now.”

• Desde niño he sentido curiosidad… = I have felt curiosity from childhood until now.

So the sentence implies:

• This curiosity started in childhood
• It continues in the present

These three tenses give different time perspectives:

• He sentido (present perfect):

  • Focus: from the past up to now
  • Desde niño he sentido curiosidad… = Since I was a child, I have felt curiosity (and I still do).

• Sentí (preterite):

  • A completed feeling in the past, not necessarily connected to now.
  • Desde niño sentí curiosidad… sounds like you’re summarizing a past period, often understood as in that stage of life, but not as clearly “up to this moment.”

• Siento (present simple):

  • Focus on the present only.
  • Desde niño siento curiosidad… is grammatically possible, but stylistically odd; the desde niño naturally invites a tense that covers past-to-present, so he sentido fits best.

In this sentence, he sentido is the most natural if you want to say the curiosity started in childhood and continues today.

You’re right that in much of Latin America, speakers prefer the preterite (sentí) more than the present perfect (he sentido) compared to Spain.

However, Desde niño he sentido curiosidad… is still perfectly correct and natural in Latin American Spanish because:

• desde niño clearly includes the idea “up to now”.
• The action/state (feeling curiosity) started in the past and is still true.

A Latin American speaker could also say:

• Desde niño sentí curiosidad por el universo.

That tends to sound more like you’re talking about a whole past stage of your life. To keep the “and I still do” flavor really explicit, he sentido works very well, even in Latin America.

He estado sintiendo curiosidad is grammatically possible but sounds unusual here. Differences:

• He sentido curiosidad:

  • Normal, idiomatic way to express a long-lasting feeling.
  • Compact and neutral.

• He estado sintiendo curiosidad:

  • Sounds more temporary, more like “I’ve been (recently) feeling curious.”
  • Often used for shorter, more limited periods, like:
    • Últimamente he estado sintiendo curiosidad por la astronomía.

For “since childhood and continuing to now,” he sentido curiosidad is the natural choice.

With curiosidad, Spanish commonly uses por to introduce what you are curious about:

• Tener / sentir curiosidad por algo = to be curious about something

Examples:

• Siento curiosidad por otras culturas.
• Tiene curiosidad por aprender japonés.

You can sometimes see curiosidad sobre (roughly “curiosity about / regarding”), but curiosidad por is more idiomatic in this kind of sentence.
Curiosidad de is much less natural here.

So:

• curiosidad por el universo ≈ “curiosity about the universe”

Both options are correct:

1. por el universo y por las estrellas

   • Repeating por slightly emphasizes that these are two separate objects of curiosity.
   • Very clear and perfectly natural.

2. por el universo y las estrellas

   • The single por is understood to apply to both el universo and las estrellas.
   • Also natural and common.

Repeating the preposition is a stylistic choice, not a rule. It does not change the core meaning.

The prepositions express different ideas:

• curiosidad por el universo:

  • what you are curious about
  • “curiosity about the universe”

• curiosidad en el universo:

  • would mean curiosity in the universe (as a location), which is odd in this context.

So por here corresponds to English about rather than for or in.

Spanish uses definite articles more often than English, especially with general or abstract nouns:

• el universo = the universe as a whole concept
• las estrellas = stars in general

In Spanish you normally say:

• El universo es enorme.
• Las estrellas son muy lejanas.

Dropping the articles (universo y estrellas) would sound strange and incomplete in standard Spanish in this sentence.

Yes, and these options are very common, especially in Latin America:

• Desde pequeño he sentido curiosidad… (since I was little)
• Desde chico he sentido curiosidad… (since I was a kid)

They all mean essentially the same thing:

• niño = child, boy
• pequeño = small / little (used to mean “when I was little”)
• chico = kid (widely used in many Latin American countries)

Remember to match gender:

• Female speaker: desde pequeña, desde chica, desde niña

Spanish normally drops subject pronouns when the verb ending already shows the subject:

• he sentido clearly tells us it’s yo (first person singular), so yo is unnecessary.

• Desde niño he sentido curiosidad… (most natural)
• Yo, desde niño, he sentido curiosidad…
  • Grammatically correct
  • But sounds marked/emphatic, like you are contrasting yourself with others:
    • Yo, desde niño, he sentido curiosidad… (pero mis hermanos no).

In neutral statements, omitting yo is standard.

Yes. Word order is fairly flexible here, and both are correct:

• Desde niño he sentido curiosidad por el universo y por las estrellas.
• He sentido curiosidad por el universo y por las estrellas desde niño.

The difference is mostly in emphasis:

• Starting with Desde niño slightly emphasizes the time frame (“Ever since I was a child…”).
• Putting desde niño at the end sounds a bit more neutral or “afterthought”-like in rhythm, but is still very natural.

They’re related but not identical:

• sentir curiosidad por algo

  • To feel curiosity about something.
  • Focus on the feeling toward a specific topic.
  • Desde niño he sentido curiosidad por el universo.

• ser curioso / curiosa

  • To be a curious person (as a general trait).
  • In many Spanish-speaking places, especially in Latin America, ser curioso can also mean “to be nosy” (to pry into others’ business).

So sentir curiosidad por el universo is a safe, neutral way to say you’re intellectually interested in the universe, without suggesting you’re nosy.