Learn Hardcore Hebrew: כשהתינוק לא רגוע, אבא מחבק אותו ומנשק אותו כדי להרגיע אותו. - When the baby is not calm, Dad hugs him and kisses him to calm him.

In Hebrew, short prepositions and conjunctions are often attached directly to the following word, so instead of writing them separately, you often get one written unit like כשהתינוק.

A longer, more formal version would be כאשר התינוק, but כשהתינוק is very natural and common.

Why is there no word for is in התינוק לא רגוע?

Because in Hebrew, the verb to be is usually omitted in the present tense.

So:

התינוק לא רגוע literally looks like the baby not calm
but it means the baby is not calm

This is completely normal in Hebrew.

Compare:

הוא עייף = he is tired
היא בבית = she is at home
התינוק לא רגוע = the baby is not calm

But in the past or future, Hebrew does use forms of to be:

הוא היה רגוע = he was calm
הוא יהיה רגוע = he will be calm

Why is it רגוע and not רגועה?