Europe in December with a toddler - need to make plans ASAP

Hi all! My husband was just invited to attend a conference in Frankfurt in December. We have decided to make it a family trip. We are experienced travelers, but have an 18 month old who has never been overseas.

Source: Travel Tips & Trip Ideas http://www.fodors.com/community/travel-tips-trip-ideas/europe-in-december-with-a-toddler-need-to-make-plans-asap.cfm