Whether you're gathering group costume ideas for a spooky Halloween party or dressing up with the kids, we have Halloween costume ideas that are perfect for adults. We've rounded up the best couple's ...
Newsweek: Halloween Couples Costumes 2018: Prince Harry and Meghan Markle, Avocado Toast, Other Fun Ideas
Halloween Couples Costumes 2018: Prince Harry and Meghan Markle, Avocado Toast, Other Fun Ideas
MassLive: Adult Halloween Costumes: Last-minute couples costumes ideas that won’t embarrass your kids or get you fired
Adult Halloween Costumes: Last-minute couples costumes ideas that won’t embarrass your kids or get you fired
"Adult children" comes from "adult children of alcoholics", but now has broader reference to adults who were abused emotionally, physically or sexually in childhood.
Merriam-Webster has an entry for half-orphan, meaning someone with only one living parent. They say specifically a child, which would match the usual usage of "orphan" (as mentioned in the question), but it might be used of an adult sometimes, either jocularly or by extension. This doesn't distinguish which parent is dead, but could be combined with a further explanation if it matters.
The best way to do it, I think, would be to forgo the hyphens completely and go with: I am a psychologist who works with children and adults. Anything else is awkward, ambiguous, or both. If it's necessary to emphasize that this individual works with children and adults (i.e., this isn't just introductory information), you could add in a 'both': I am a psychologist who works with both children ...