Learn Spanish (Latin America): El niño duerme silenciosamente en la cama.

It comes from the adjective silencioso (silent). To make an adverb ending in -mente (which works just like '-ly' in English), you first change the adjective to its feminine form, silenciosa. Then you add -mente to the end, giving us silenciosamente.

Why is the verb duerme and not dorme?

The infinitive verb for 'to sleep' is dormir. This is a stem-changing verb, which means the o in the middle changes to ue in the present tense for most subjects. Because we are talking about el niño (he), the verb changes to duerme.

Does silenciosamente have to go right after the verb?

Not necessarily. Adverbs are pretty flexible in Spanish. While putting it right after the verb (duerme silenciosamente) is the most common and natural-sounding choice, you could also say El niño duerme en la cama silenciosamente.

Why does it say en la cama when English usually just says 'in bed'?

In English, we often drop the word 'the' for general locations like 'in bed' or 'at school'. Spanish prefers to keep the definite article (la) for these places, so it is much more natural to say en la cama.