The cast is expanding on The Spiderwick Chronicles with Nick Nolte, Martin Short, Joan Plowright, Izabella Miko, Andrew McCarthy and Mary-Louise Parker announced just today.

According to Empire they will be playing:

Mary-Louise Parker is currently negotiating to play the three central kids’ mother, who sends them to live with family after suffering exhaustion following a difficult separation from her husband (Andrew McCarthy)...

...Nick Nolte and Martin Short, who will voice supernatural creatures Mulgrath, an evil shape shifter looking to snatch the kids and Thimbletack/Bogart a creature that can protect or disrupt a household, depending on its mood. Joan Plowright will play the children’s’ aunt, who’s packed off to an asylum because she – and no one else – can see the creatures...

...The Foresaken’s Izabella Miko, cast as the leader of a group of elves.

With David Strathairn already announced it's looking like a solid cast with some strong highlights. I have to say I like Miko as an elf, have you seen her face? She's perfect.