Ryan is absolutely right about these kids getting a chance to enjoy these animals. It's very important not to make assumptions about them just because they have a disability. Obviously you need to know about the kids a bit (disabled or not) and be reasonably sure they aren't irrationally violent or wreckless. My daughter has been handling snakes since she was three. It doesn't take a whole lot of intellectual capacity to understand "GENTLE". Also, as with any minor, you may want to have a telephone conversation with the parents about the whole thing, I'm not sure a support worker or teacher necessarily has the authority to make that choice. Of course the whole thing is kind of stupid because no one would think twice about letting a kid pet a cat. A cat can be hurt by a child (I've seen that more than once) and child can also be hurt by a cat. What's the difference? How much money would a lawsuit about a couple of cat scratches bring? Could a bite from a 20" BP be any worse than that?
I feel a little light headed... maybe you should drive...