There are already more than 10,000 people registered for Family Discovery Day at RootsTech 2016. I would strongly suggest that if you want to attend this event, that you register now. It is very likely that registration will be maxed out some time before the event.
Here is the description from the RootsTech 2016 Website
In addition to RootsTech, families and members of The Church of Jesus Christ of Latter-day Saints are invited to attend Family Discovery Day at RootsTech on Saturday, February 6, 2016. This free one-day event is a day of inspirational messages, instructional classes, interactive activities, and exciting entertainment to teach LDS members (ages 8 and up) how to find their ancestors, prepare and take them to the temple, and to teach others to do the same.