Nursing jobs with Mentally Challenged children?

I want to be an RN and I was wondering if there was any specific field that I can be an RN that works with Mentally challenged children. I have a cousin who has down syndrome and love taking care of her and also other children with down syndrome, autism, etc. Any info would be greatly appreciated. Thanks!! :D

View this post on my blog: http://travelnursesuccess.com/nursing-jobs-with-mentally-challenged-children