Is it possible to forget about a childhood trauma and have the memory reappear in your teens? Could it even be a false memory?

Yes. Memories are continuously being adjusted in order to remain in our consciousness. We can repress painful memories, which are then remembered when triggered by a similar sensory or emotional experience. I suggest seeing a therapist capable of working with these issues.
Possible. Both are possible. It could be a repressed memory or it could be a false memory. An evaluation with a good therapist can help you distinguish between the two.