yep best solution (proven over 14 years long daycare) butter knife, let playdough dry, srape dry dough loose with knife (watch your eyes as small flecks of playdough in the eye stings like nothing else!!!! speaking from lots of experience LOL) then Vacum up.
putting a mat or piece of plastic down under the tablew will help a little till it gets stuck on someones shoe and finds it's way in to the carpet anyway...good luck!!