Papersource has great crafting workshops for scrapbooking, cardmaking, paper flowers, bookbinding, and more. They carry beautiful papers, cards, and a ton of other stuff for crafting. The classes aren’t for kids, but they would be fun for a girls’ night out. They have locations in Boston, Brookline, Cambridge and Wellesley.

As an aside, based on one of the comments posted below, I wouldn't suggest shopping at Papersource for craft supplies for kids; for that, I would recommend one of the chain craft stores like AC Moore.  But I would recommend Papersource for their blank cards, which are excellent quality, and their papers, as they have a much more extensive collection than the chain stores.