O soldado foi gentil com a criança.

In Portuguese, it is very common to use the definite article before a noun, especially when talking about a specific person or thing.

• o soldado = the soldier
• soldado by itself can sound more general, dictionary-like, or less complete in a normal sentence

So O soldado foi gentil com a criança sounds natural and complete.

Here, foi is the past tense of ser.

• ser = to be
• foi = was

So in this sentence:

• O soldado foi gentil = The soldier was kind

A common point of confusion is that foi can also be the past tense of ir (to go). Portuguese speakers tell the difference from context.

Here, because gentil is an adjective, foi must mean was, not went.

Gentil is an adjective that often has the same form for masculine and feminine singular.

So you can say:

• o soldado foi gentil
• a mulher foi gentil

The adjective does not need to become gentila or anything like that.

In the plural, it does change:

• os soldados foram gentis
• as crianças foram gentis

So:

• singular: gentil
• plural: gentis

In Portuguese, gentil is commonly followed by com when you say who someone was kind to.

• gentil com alguém = kind to someone

Examples:

• Ela foi gentil com ele. = She was kind to him.
• Eles foram gentis com a professora. = They were kind to the teacher.

Even though English uses to here, Portuguese uses com.

So:

• gentil com a criança = kind to the child

Because criança is a feminine noun in Portuguese, no matter whether the child is male or female.

So you say:

• a criança
• a criança pequena
• a criança foi gentil

This grammatical gender belongs to the word, not necessarily to the real-life sex of the person.

Other examples like this exist in Portuguese too.

If you want to make the child’s sex clear, you would usually add extra information, for example:

• a criança, um menino = the child, a boy
• a criança, uma menina = the child, a girl

Because the sentence uses com, not a.

• com a criança = with / toward the child

The form à happens when the preposition a combines with the feminine article a:

• a + a = à

But here we have:

• com + a = com a

There is no standard contraction here.

So the correct form is:

• com a criança

not

• à criança

In standard modern Brazilian Portuguese, com a normally stays com a.

So you say:

• com a criança
• com a professora

You may sometimes see older or literary forms like coa, but they are not normal in everyday Brazilian Portuguese.

For a learner, the safe choice is:

• com o
• com a
• com os
• com as

without contraction.

Yes, but it changes the nuance.

• foi gentil usually means was kind in a completed event or situation
• era gentil usually means was kind in a more descriptive, ongoing, or habitual sense

Compare:

• O soldado foi gentil com a criança.
  The soldier was kind to the child.
  → maybe in one particular moment or situation

• O soldado era gentil com a criança.
  The soldier was kind to the child.
  → maybe regularly, or as a general description in the past

This is a very common contrast in Portuguese: pretérito perfeito vs. pretérito imperfeito.

Because prepositions do not always match word-for-word between languages.

In Portuguese, com often appears in expressions where English uses to, especially after certain adjectives.

So with gentil, Portuguese says:

• gentil com alguém

while English says:

• kind to someone

This is just something to learn as a pattern.

A rough Brazilian pronunciation is:

• cri-AN-sa

A few key points:

• ç sounds like s
• ã is nasal, so the sound comes partly through the nose
• the stress is on an

So criança sounds roughly like kree-AHN-sa, but with a nasal AHN.

Also:

• cri sounds like cree
• ça sounds like sa

The normal and most natural order is:

• O soldado foi gentil com a criança.

This is the standard subject + verb + complement order.

Portuguese can change word order in special contexts, especially in writing or for emphasis, but for learners, this sentence is best kept in the normal order.

So this is the form you should use first.

Yes, but the meaning changes slightly.

• gentil = kind, nice, gracious, polite depending on context
• educado = polite, well-mannered
• bondoso = kind-hearted, benevolent
• amável = lovable / kind / amiable

So:

• O soldado foi gentil com a criança.
  sounds natural for was kind / nice to the child

If you specifically want polite, educado may fit better in some contexts. If you want deeper kindness, bondoso may fit better.

Because the verb agrees with the subject, not with the object or complement.

The subject here is:

• O soldado

So the verb is singular:

• foi

The phrase com a criança is not the subject. It just tells us who received the kindness.

If the subject were plural, the verb would change:

• Os soldados foram gentis com a criança.

So the agreement is:

• O soldado foi
• Os soldados foram

A few possible plural versions are:

• Os soldados foram gentis com a criança. = The soldiers were kind to the child.
• O soldado foi gentil com as crianças. = The soldier was kind to the children.
• Os soldados foram gentis com as crianças. = The soldiers were kind to the children.

Notice the changes:

• o → os
• a → as
• foi → foram
• gentil → gentis only in the plural

So gentil changes only when it becomes plural.