If you are above average intelligence, your children will, on average, be more intelligent than average. They will also, on average, be less intelligent than you. This is an example of so-called regression to the mean. It's easy enough to see why it has to be so. (But I'll leave it as an exercise for you above-average-intelligence people.)
My children are smart, but not as smart as me. My grandchildren are also smart, although not as smart as their parents. Regression to the mean. Just a fact of life.
I love my children more than life, and my grandchildren even more. My children are all doing fine: well-educated, good jobs, decent partners, lovely children, happy. My grandchildren also all seem set fair (assuming we can stop burning the planet down, but sadly that's another matter). Why are they doing so well? Well, they have always - and explicitly, overtly - been loved ...
Intelligence, shmintelligence: what's it matter so long as your mummy and daddy love you?
(OK, OK, I know ... random illness, accidents, Tory governments: things can go wrong. But do the best you can. Love your children, let them know you do ... they'll be OK. Try not to worry.)