I found these two references which are in agreement:
1. On youtube: https://youtu.be/APKXNPQrv_s
2. shortened http://goo.gl/arVv9E
To remove PLAY-DOH compound from carpet or fabrics, allow it to dry completely, and then loosen with a stiff brush. It may be necessary to vacuum clean or wash with gentle soap and cold water. You may need to repeat the process in order to completely remove the PLAY-DOHcompound.”Jun 4, 2013
Good luck and let us know how it goes.(don't forget a post cleaning photo)
I'm no chemist, but given the ingredients of playdoh, I think an oil may compromise the colour of the carpet.
.. though I have heard that peanut butter (with it's oil) is excellent for getting chewing gum out of hair. ... bu then that's a different problem entirely.
I agree, it needs to be made cold to turn it hard and brittle - I think you can try hitting it with a hammer as well, and then vacuuming up the pieces.
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try eucalyptus oil. Its good for sticky things
Aw come on... Is that the worst of it? Or have you yet to discover the green goop has reached further then expected? Embrace the play dough years before they turn into the craft glue or nail polish years! Good luck with which ever method you choose. Ask on some parenting forums also.
Is it a 100% wool carpet? Allow to dry and brush gently to break up bits and vacuum. Then go over the area by holding a steam iron over the top of the wool (about an inch above). Pulse some steam through it. This tends to plump up the wool fibres and allow the remaining dough to break loose. Then allow to dry and vacuum again.