Wisconsin is a nice destination to visit as well as a nice place to live.But sometimes the weather conditions will be abnormal and during January, the weather will be very cold, so better ask your parents to check the weather before they pack. December is a snowy month and January is less compared to Dec, but still a little above normal. I had an exciting experience at Madison, the capital of Wisconsin and a fabulous city of North-America. Your parents have chosen a good place to have the birthday party:)
Many of the Wisconsin's cities offer variety of hotel, motel and lodging options and especially at Madison I found good choices of hotels. I was staying at Howard Johnson hotel which is one of the best
hotels in Madison and the services were excellent. You didn't mention about the city in which your parents are interested to stay, however, just check out
Wisconsin hotels page for more information on hotels in major cities of Wisconsin.
It's very nice to have a vacation in Wisconsin as it offers many things to do including beach life, water sports, vibrant nightlife, camping, snow-sports etc., Convey my best wishes tour parents to have a wonderful Wisconsin vacation !