It is awful. It appears to have once been intended to be a walk-through but it wasn't when I was there, and it's actually not large enough to be a good walk-through. This is the best viewing angle there is of the exhibit.
This is the worst section of the children's zoo, and I've been to Point Defiance Zoo at least 5 times in the past couple of years and I've never seen any visitor in with the wallabies.