One of the most effective ways of getting into the Christmas spirit is to visit the local Christmas market. The Sims are no different. At their local market the kids can play with their friends, while mom and dad does some gift shopping (well, not really, but at least they can admire the stuff on display). Then of course they can have some mulled wine at the little bar, even though the barman might call it something else. You will find some good quality Christmas trees there (not for purchase) but the greatest of them all, obviously, is in the middle of the square.
