Want to turn mermaid back to human. Please help!!!

My sim had a baby with a female mermaid, and now the baby is a mermaid as well. He is a child now and I can't get the "adapting to land" moodlet no matter how long he is away from the ocean. I would try the potent cure elixir, but Supernatural happens to be the one expansion that I don't have :( is there anything else that can be done to make my sim normal?