I would train a LoRA, here's a guide (also has links to other guides at the bottom)
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Ok . . . so I have a Mac M2. And have been using Diffusion Bee to avoid the terminal. But I'll see if I can figure it out.
Much simpler way, even if not as cool: try https://apps.apple.com/app/id6444050820 that is free and great. First download a model, if you already have one you like just use the Civitai.com link, otherwise there's a selection of them and I'd try... Realistic Visions? The 8 bit one saves you a little space. Then use the photo icon in the bottom to import a photo, you want something with the face clearly visible. Use the eraser to get rid of everything other than the face. Now try prompting for an astronaut! Should work already but you can try adding Controls: Tile, Inpainting and Pose specifically.
Performance wise you can go at the bottom of the left side, click on the cpu looking icon and select (if it's not selected already) Use CoreML: Yes and for the CoreML compute units go with All.
My M2 Mini takes a dozen seconds for a normal generation like that. With the Control modules and Inpainting is going to be a little slower obviously but hey, it's a fast app.
The easiest way is take a picture of your son and "inpaint" the parts that are not him with the style you want. The more difficult way would be to train a LORA. Here is a blog by someone who did exactly that. https://www.shruggingface.com/blog/self-portraits-with-stable-diffusion-and-lora
I found this repo that may help here
If you’re still stuck though, I’ll happily figure out how to do and give you the steps to take. I’m not home at the moment so will be sometime over the weekend.
In-painting. You can selectively generate some parts of an image. So you can take pics of your son and generate the parts he isn't in.
Roop is what you are looking for. MUCH simpler than creating a LORA. https://youtu.be/8SWon8erHZw?si=XKFDvXh0sJhF6I1D
And if you haven't subscribed to Olivio Sarikas's YouTube channel, you should
Here is an alternative Piped link(s): https://piped.video/8SWon8erHZw?si=XKFDvXh0sJhF6I1D
Piped is a privacy-respecting open-source alternative frontend to YouTube.
I'm open-source, check me out at GitHub.