Booking Form

Hello, from the demo of your theme, the booking form in the tours has a functional calendar that allows the user to pick a date when making a booking, but in my site, the booking form has an inactive calendar. What could this be that is causing this error?
I would like the calendar to function too.
Attached is the url, you can see the calendar is inactive: http://www.adventurebackpackers.net/tours/3-days-lake-manyara-ngorongoro-crater-safari/