Effects of untreated knock knees in kids? Do they grow straight, before reaching adulthood?

Maybe. The expected pattern is for kids to be a little bow legged at 1-2, somewhat ,knock need at 4 an d getting straighter by six or so.
Normal anatomy. Most likely your child looks like one of you, and if you stood them next to you and looked in the mirror, you'd see the legs bending in like yours or your husband's. A small amount of knock-kneed appearance is normal. Most have it. Some have it more. However, if there's normal athletic performance, and no pain, it's not a great concern.