I don’t think most anorexic patients are childlike or fear being in an adults body.
No, I don’t think so either. While there are a number of ways children and adolescents get to anorexia (and these factors need to be considered with treatment) starvation creates its own mental health issues, including social withdrawal.
There’s that fascinating study done on healthy college men where they starved and then refed them. They became mentally unwell and displayed disordered thinking around food with this persisting into the refeeding stage.