Moving to Santiago with kids (Santiago de Chile)

Hi everyone,
My husband and I are moving to Santiago october 1st. With have two little girls, almost 4 years and 6 months.
I have never been to Santiago, can anyone give me some tips for any kids activities or something? I wish for my 4 year old, that she meets other kids soon, because she's used to have many friends around her..
Maybe anyone knows about ballett classes or music classes or anything like that?

Thanks.

Melanie