I live on the reservation and i have two cats...?

Well, actually three cats; The Momma cat, and two little ones. The little ones were born April 5th 2011. The momma cat uses the bathroom outside and the two little ones started using the bathroom in the litter since they were born or whatever.. anyways, I was wondering if there is any way i could 'teach' or 'train' them to use the bathroom outside.