Ralda on "[Plugin: Contact Form 7] Datepicker"

I tried it like that but it doesn't work. What am I doing wrong?

The contact form looks like this:

[date* geboortedatum min:2013-01-01 max:2013-12-31 step:7 class:required "yyyy/mm/dd"]

I added the line in the Functions.php but after saving the line was gone. I must have placed it on a wrong line. Can anyone tell me were to place it?

Here's my contact form with the non-working datepicker: http://www.spellenmolen.be/testpagina/