Learn Spanish (Spain): El niño se levanta tarde.

se is a reflexive pronoun. The dictionary form of the verb "to get up" is levantarse. In Spanish, daily routine actions like getting up or showering are often treated as things you do to yourself. Literally, the boy "raises himself". Since "the boy" is a third-person subject, we use the pronoun se.

Why does se go before the verb levanta?

In Spanish, reflexive pronouns like se are placed immediately before the conjugated verb. That is why it is se levanta and not the other way around.

I thought tarde meant "afternoon". Why does it mean "late" here?

It means both! As a feminine noun (la tarde), it means "the afternoon". But in this sentence, it is used as an adverb to describe when the action happens, which translates to "late".

What would the sentence look like if it was "I get up late"?

It would be Me levanto tarde. You remove El niño, change the reflexive pronoun se to me (myself), and change the verb ending to the "I" form, which is levanto.