The little girl who plays Sheldon’s sister on Young Sheldon looks oddly like what I’d imagine Dan and Amy’s kid to look like
I can see that – though whether the kid ends up with blue eyes will depend on whether Dan carries the recessive gene or not. Though the other aspect is… the child having blonde hair as a toddler (or even a youngish child), doesn’t necessarily mean she’ll be blonde (or dark blonde, in the pic above) for life. Hair darkens after all.
(This drove me mad when they tested Richard III’s dna after finding the body, and there was all this shock and surprise that he may have been light-haired as a child. It’s pretty common among at least Northern Europeans (and possibly among Southern Europeans too, I don’t know) for that to be the case – I’m pretty black Irish myself, but I had blonde ringlets as a toddler. It’s not in the least bit unusual).
It does strike me that…Veep is a little bit unlucky in that…everyone knows what Anna Chlumsky looked like as a child, so it’s much easier than it usually is for the audience to do the comparison with anyone they cast as her offspring. But to be honest, I give considerable leeway to shows when casting families, and especially when casting young children. From what I’ve heard, below the age of about five or six, actors tend to treat child actors almost as props, because it simply isn’t fair to expect them to be capable of anything more than that. Mad Men’s success with Kiernan Shipka really was a one in a million chance – she looked like both her fictional parents and she could act.