I didn't know until well into adulthood. I felt like I was the only person in the world who felt like I do, and I never could understand what was wrong with me. It made life painful, difficult and I often felt ashamed for my sensory issues. If I had known there was a reason and I wasn't just somehow defective, I believe my self-esteem as a child would have been much better. IF my parents had handled it properly. My mother has a way of talking about things as if they're so horrible she cannot even speak of them. Most are referred to as that thing, and so forth.
Talk about it now. Talk about it often. Don't make a big deal of it, just present it as fact in a non-emotional manner so there's no emotion attached to it. We discuss it regularly around here, and our kids ar 4 and 2.
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They tell me I think too much. I tell them they don't think enough.