I don't tend to mention EL much. My son is only sounding out CVC words (and only IF he wants to, which considering he won't even talk in front of adults he doesn't know, is rarely) so doesn't come across as super-advanced on the reading front - I have talked to other parents at playgroups and said that he has shown a great interest in letters and their sounds that I simply encourage and they show no more interest. I think if I told them what we do they'd think I'm being pushy and 'forcing' him to learn
He is much more 'advanced' in Maths, Music and Fine Motor, which are less noticeable. Everyone assumes that the fine motor skills are a side effect of taking so long to walk - he spent a lot of time in one place practicing. While this is true, it is not the *only* reason.
People are always amazed that he holds a pen correctly - they don't realise how much easier it is to simply not allow him to get in the habit of holding it incorrectly!
Maths never gets brought up (as he doesn't talk in front of others) and Music is 'just singing' as far as they are concerned.
In terms of my family, I don't tell them much. They know how about his reading, but as we were all reading pre-school my Mum doesn't consider it overly 'advanced'. They know he counts, but I haven't mentioned we are doing a K-level textbook. My Mum thinks anything beyond learning numbers (and perhaps memorizing some times tables songs) is 'too much' because "otherwise, what will they learn in school?"
She often rants at my cousin's boasting that her nearly-5 year old is doing age 5-7 maths workbooks and is 'so advanced' because Mum thinks we should leave it to the teachers, lest they become bored.
So, pretty much only my best friend knows, and I hope to share EL more completely with her when she eventually has her own children.
Honestly, if it weren't for the encouragement of this forum, I might have done a lot less with my son. As it is, I don't feel that I can ever do enough