SSRS Report Builder can't figure out how to set up parameters correctly

I have a simple stored procedure that has 4 date parameters @startdate, @enddate etc. They show in Report Builder but I can't figure out how to get the report to call them and force the user to enter their dates.

Second question is that my dates are unfortunately varchar(8) so I'm not sure how that will work in regards to entering dates in the parameters on the report server as 20150101?

CREATE PROCEDURE [dbo].[Dental_Assessment]
(

@dobstart	VARCHAR(8),
@dobend		VARCHAR(8),
@servdatestart   VARCHAR(8), 
@servdateend   VARCHAR(8) 
)
AS

select distinct pp.person_id, p.last_name, p.first_name, p.person_nbr,p.date_of_birth  from 
patient_procedure pp 
inner join person p on pp.person_id = p.person_id
where pp.cpt4_code_id in ('D0191','D0120','D0145','D1050','D1080', 'D0140', 'D0160', 'D0170', 'D0171')
and p.date_of_birth between @dobstart and @dobend
and pp.service_date between @servdatestart and @servdateend

reportbuilderparameters.png