Answer:
Antes los niños VIAJABAN (viajar) con poca protección en los carros, pero ahora siempre llevan cinturón de seguridad.
Step-by-step explanation:
Viajar is in infinitive, it means travel.
In this case, the work "antes", which means "in the past" makes reference to an action that took place in the past and ended in the past. Therefore you need to use the simple past, in spanish it's called pretérito perfecto simple.
As the sentence refers to "los niños" or "the kids", we know it is third person plural.
So the correct conjugation is VIAJABAN.
Los niños viajaban = They traveled