It's hard. One of the most difficult parts of this job I think.
Especially when you see there could be a problem and the parents are in denial, don't want to make the effort, are scared, etc. What would they do if their child's doctor made suggestions? Wouldn't they follow up on it? If not, and considering how much help their child needs, should the state(or someone else) step in? It's just hard.
I guess in a situation like yours, I'd care for them the very best I could and if it wasn't enough, I'd tell them why and end the business relationship.
The detaching I find the most difficult is when they age out, move onto preschool
or when the parents plain and simple take them out, and we've always had a great relationship.
I know it happens but that's the tough thing for me to take.