son vs están
ellos (son o están) muy activos
2 Answers
In any event, both are correct. It just that the meaning depends on context.
Katy:
You already know the meaning of ser and estar. So, with that in mind I am going to say stuf in English.
The volcanoes are active in this very moment.
The volcanoes in this area are very active.
Same thing with kids, for example.
Would that help any?
Review this part of the website for estar:
And this part for ser
And this part for contrasting the 2:
This looks like homework. Edit you initial question with a choice and why and someone will help you.