Learn Spanish (Latin America): El niño lee un libro y la niña come pastel. - The boy reads a book and the girl eats cake.

y means "and." It is a coordinating conjunction, which is a grammar term for a word that connects two equal parts of a sentence. Here, it simply connects two complete thoughts: El niño lee un libro and la niña come pastel.

Why do both lee and come end in -e?

Both lee (reads) and come (eats) come from regular verbs that end in -er: leer and comer. When talking about "he" (el niño) or "she" (la niña), you drop the -er ending and add -e.

Why does the sentence say un libro (a book) but just pastel (cake) without un?

Just like in English, Spanish often leaves out words like un or una when talking about an unspecified amount of food. Saying la niña come un pastel would mean she is eating one whole, entire cake! Saying come pastel simply means she is eating some cake.

How do the words for "the" change before niño and niña?