I'm thinking of excluding our friend's son from being in our photos.
Why? Is there a reason behind not wanting your friend's son in your photos?
Yes, his son looks and seems like a psycho.
Even if you think your friend's son is off putting, you shouldn't prevent him from being included in the photos that you take. Excluding someone from being in a photo is very rude and inappropriate behavior and can be emotionally damaging to the person being excluded. You should ensure that your friend's child remains welcome whenever you take a photo and also be more open minded and stop thinking that his physical appearance or mannerisms are odd.
You're right. I don't want to make a big fuss anyway.
That is also a good reason. Your friend would most likely be upset.