In the wild, iguanas use high perches, swing their tails over the edge and let fly. I had a pet iguana climb 12 feet up a large indoor branch and while I watched he swung over and let splat UGH. I took the limb away. IMO it's natural behavior. At least he is not trying to poop onto your son when he is near.
I had a rabbit that flung his urine at me when I approached his cage. But he was a good sire so I held my patience. I've seen Lorikeets aim at people on the fly, and toucans do it too, both just for fun. They like to check out the screechy reactions. Let's hope that Oscar doesn't discover the fun in his behavior LOL.