Update children_count

Hello,

I have an ‘acts_as_tree’ model.
I did not use counter_cache, and did not have ‘children_count’ field in
the
table.

Now I decided to use it and created the field.
But I is only incremented to new records…

I was wondering if there is a method or a way to automagically update
all
existent records, or I have to do it manually.

Thanks,

Parra