There’s no way for this to sound not like a humble brag. I’ll caveat by explaining, I have three children, and have not experienced anything like this until the youngest. My kids have several cousins, they are also not like this.
My oldest child is quite bright but quite lazy and uninterested in school work, he wants to do a trade, isn’t interested in further study, which is fine. He also has ADHD. So his marks and school work are all over the place. My second child is quite average, performs straight down the middle, is quite creative but again, not academically focused and nothing out of the ordinary school wise, and did briefly require learning support. In summary, I’m not a crazy person who thinks all of her children are brilliant geniuses.
We have a youngest child who turned 2 in March. So this is very young. She was drawing the other day and wrote a perfect letter e. She called out:”Mummy, look, e!” I couldn’t believe it, so rubbed it out and asked her to do it again. She did, perfectly. I then wrote down a series of letters and asked her what they were, she got them all correct, I varied upper and lower case. We also have read her a book about shapes, maybe 3 times. She points them all out correctly in the environment, including more advanced ones like “diamond”. She knows big, medium and small (but does call them Daddy, Mummy and baby, like baby cow for a calf and Daddy cow for a bull). We do baby dancing, and she knows and correctly does all of the choreography. She anticipates it and does it in advance, she remembers it. They’ve moved her in with older kids at nursery for learning groups and the dancing teacher has put her in the class with 4 year olds.
Is this normal? I don’t think it is. My other children knew their letters by the time they started school, but only just, and they could write their names but not really other words or letters. That seemed to be normal amoungst their cohort.
What should we do, if anything, to support this? Previously I’ve provided toys, lots of outdoor time and we always had a bed time story, but my other kids mainly liked running around, imaginary play and destroying the house. 
This child will sit and complete puzzles and activity cubes. She draws and draws and leads through books. She observes what I’m doing and comes to help and she is helpful! She realises the goal of any activity (like taking the washing out of the machine) and does it until it’s done. She watches once and knows how to do things correctly. She can navigate the Netflix to find Shaun the Sheep for example.
I feel as though she could have some support to really extend herself. At the same time, she is a baby in nappies, and I’m very much not a flash card drilling kind of Mum.
My brother is highly intelligent, he was skipped ahead in school and it resulted in a mental health crisis for him, so there’s that.
What do people do in this situation? Maybe learn an instrument? Language class or something? I don’t know. In other areas she’s totally just turned two: still in nappies, has a baby voice and baby grammar, ie sounds her age when she talks.