Copilul își spală părul.

Because Romanian usually puts the definite article at the end of the noun.

• copil = child
• copilul = the child

So -ul here means the.

This is very different from English, where the is a separate word placed before the noun.

For the same reason: -ul is the definite article.

• păr = hair
• părul = the hair

In this sentence, Romanian uses the definite form because it is referring to a specific thing: the child’s hair.

Își is a reflexive/dative clitic. In this sentence, it shows that the hair belongs to the subject and that the action is directed toward the subject’s own body.

So își spală părul means something like:

• washes his/her own hair
• literally, roughly: washes the hair to himself/herself

English usually uses a possessive adjective here: his hair or her hair. Romanian often uses this reflexive structure instead.

Because Romanian often prefers a reflexive construction when someone does something to their own body or personal belongings.

So instead of saying:

• the child washes his/her hair

Romanian commonly says:

• Copilul își spală părul

The idea of his/her own is already built into își.

Not exactly.

• se spală = washes himself/herself
• își spală părul = washes his/her hair

So:

• Copilul se spală. = The child is washing himself/herself.
• Copilul își spală părul. = The child is washing his/her hair.

With își, the focus is on washing a body part or possession of one’s own.

Because Romanian unstressed pronouns like își normally come before the conjugated verb.

So the order is:

• Copilul = subject
• își = clitic pronoun
• spală = verb
• părul = object

This word order is very normal in Romanian.

Spală is the 3rd person singular present form of the verb a spăla (to wash).

So:

• eu spăl = I wash
• tu speli = you wash
• el/ea spală = he/she washes

Here it matches copilul, which is singular.

Because Romanian present tense can often express both:

• a general action: washes
• an action happening now: is washing

So Copilul își spală părul can mean either:

• The child washes his/her hair
• The child is washing his/her hair

The exact meaning depends on context.

Grammatically, copil is a masculine noun, so copilul is masculine in form. In many contexts, though, it can simply mean the child without strongly focusing on sex, depending on situation and context.

If Romanian wants to be more specific, it might use:

• băiatul = the boy
• fata / fetița = the girl / the little girl

So this sentence by itself may or may not make the child’s sex important, depending on context.

A simple approximation is:

• î = a close central vowel, somewhat like a very tight, neutral vowel; English does not have an exact equivalent
• ș = sh
• so își sounds roughly like uhzh or eesh only very approximately, but neither is perfect

More exactly, it is one syllable: îș plus a very short final i sound that softens the consonant.

If you are a beginner, the most important thing is:

• ș is always like English sh
• î is a special Romanian vowel with no exact English match

Yes. Romanian has other ways to express similar ideas, but Copilul își spală părul is a very natural way to say it.

For example:

• Copilul se spală pe cap. = The child is washing his/her head/hair area.

But this is not exactly the same.
Își spală părul specifically focuses on the hair.
Se spală pe cap focuses more on washing the head area.

So the original sentence is the most direct way to say The child is washing his/her hair.