It is not always a correlation. And if you're both high achievers it can feel like you'd expect your dc to just fly academically like you did.
But it's a humbling day when you realise that your dc are indeed individuals. Please never let your disappointment show.
My dd is dyslexic and so struggles with some aspects of traditional academics. It's shit enough for her to have to get through 14 years of schooling having to work so much harder, when her brother is sailing through with what appears to be very little effort.
My dh found it harder than me to accept, he worries she won't be as successful -financially mainly. After a little adjustment (from him mainly, which he never let on) we both support her in what she is good at and get her as much help as we can to help her pass "academic" subjects too. She's so bright and loves to learn, I wish she found it as easy as we did, but we love her and are proud of her for who she is, even if that means may follow a different path to us (or not, who knows, it doesn't matter).
I'm sure you are supportive yourselves, and 6 is so young anyway, but if your dc isn't like you and your dh that's just as awesome.
Love the children you have, not the ones you wanted, as they say.