It's not just about reading music. It's about the proper way to hold one's hands on the piano and the proper way to do the fingering. I am not trying to sound like a snob here, but watching someone play who has terrible form reminds me of a kid who was never taught proper handwriting skills, and holds the pencil with their hand almost upside down, or holds the pencil inbetween the wrong fingers or with their fist. You see it and you know that it just exhausts that child to write like that and they look terrible doing it to everyone around them. Same thing for piano.
You can't play any more advanced music with poor form. Your children won't go very far if you don't get them someone who knows how to do it and teach it.
If your kids are willing for you to teach them, don't go it too long by yourself. If one of your child takes to it, make sure someone teaches her the right way to play so that she actually can get farther along.