Learn Italian: Siccome il tempo era brutto, il bambino si è ammalato. - Since the weather was bad, the child got sick.

The word siccome (since/because) is used when you want to put the cause at the very beginning of the sentence. If you want to use perché, you generally put it in the middle: Il bambino si è ammalato perché il tempo era brutto.

Why do we use era for the weather, but si è ammalato for the child getting sick?

This is a great example of how Italian mixes past tenses! Era is the imperfetto tense, used here to describe an ongoing background condition ("the weather was bad"). Si è ammalato is the passato prossimo tense, used for the specific, completed event ("the child got sick") that happened during those conditions.

Why does si è ammalato use è (is) as a helper verb instead of ha (has)?

The verb for "to get sick" is ammalarsi, which is a reflexive verb. In Italian, all reflexive verbs must use essere (to be) as their helping verb in the past tense, rather than avere (to have). Because it uses essere, the ending of the verb also changes to match the subject, which is why it ends in -o for il bambino.

How do I know if il tempo means "the time" or "the weather" here?