Learn Spanish (Latin America): Los niños están escondiendo los juguetes.

The verb is esconder (to hide). Because it ends in -er, we drop the -er and add -iendo to make the "-ing" form (the gerund). Verbs that end in -ar get -ando instead.

Why do we use están here instead of son to say "are"?

To talk about actions happening right now, Spanish uses the present continuous tense. This is always made by combining the verb estar (never ser) with the "-ing" form of the action verb.

The translation says "The boys", but can los niños also mean "the children"?

Yes! In Spanish, the masculine plural los niños means a group of boys, but it is also the default word for "the children" if it is a mixed group of boys and girls.

Why is there a "u" after the "g" in juguetes?

In Spanish, the letter "g" sounds soft and raspy (like an English "h") when it is right next to an "e" or an "i". To make it a hard "g" sound (like in "guest"), you have to add a silent "u" in between.