Calling Step-Dad “Dad”...Father’s Day gift


My SO and I have been together since my daughter had just turned 2, so she doesn’t remember life without him. She’s going to be 9 this year and we now have a son together (almost 5 months old). My daughter recently asked me if she could maybe start calling him something in the line of “Dad” because she doesn’t want her and her brother calling him something different. She already has a dad whom she refers to as dad or daddy so we want to think of something different. I suggested maybe we come up with a little gift for father’s day where she can ask him if she can call him dad and she was really excited to do that, but I cant think of what we could do. Anyone have ideas of how we could ask him and also give some suggestions for alternate names for “Dad”? I think I’ll let the two of them choose his name together but some ideas would be great 😊