See the cuddly giant pandas looking after their 4-month-old cub so tenderly? Now, look again. The adults are actually scientists wearing panda costumes, grinning and bearing it to make sure the cub ...
The Star: Japanese studio creates ‘Ferrari’ of panda costumes to help promote Hong Kong’s bears
The “Ferrari” of all giant panda costumes will join 2,500 bear sculptures on the Avenue of Stars in Tsim Sha Tsui on Saturday, interacting with visitors and helping to promote the real deal at Ocean ...
Japanese studio creates ‘Ferrari’ of panda costumes to help promote Hong Kong’s bears
New York Post: Researchers don costumes to aid panda cub’s introduction into the wild
"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 ...