As a parent of a disabled child, I understand that people might feel uncomfortable talking about disability for fear of offending, or just because of a fear of the unknown. Parents such as me haven't always been parents of disabled children - we've been where you are!
So please talk openly - just ask. Nobody can think badly of you for trying to learn more. Parents will help you out if needed, nobody will take pleasure from watching you squirm. Just trying to be inclusive will be appreciated.
As far possible, I believe children with disabilities should be integrated into normal schools and normal life in general - we can't change attitudes by segregating our children into 'special' schools and groups. When disabled people are as visible as 'typically able' people, then things will begin to really change.