A toy camera is any camera you would be willing to hand over to an unsupervised child and not worry about the child or the camera being harmed. I would not put the Holga into that category, I don't believe that a Holga could take the punishment a child can dish out.
Fisher Price made a lot of really great cameras for kids over the years.
You would be surprised what passes for "toy" at my house, my kid has a Kodak cameo Motor EX (possibly the last folding camera Kodak ever made, it has a plastic folding bellows), a Canon WP-1, and a National Geographic half frame binocular camera that I let her run free with. She also has a Nikon N65, that she only uses under parental supervision. As for my equipment, she is only allowed to use the cameras that she can hold by herself and look through the viewfinder, the only cameras she can't use now are the F4 and the Pentax 6X7, and always supervised.