You might want to wait a bit, but you don't have to wait 13. I think Paul tought his kids to PR when they were 8 or 9 yrs. old.
A year ago, while browsing the Net, I have stumbled upon a speed reading site, which outlined a program for children from 8 to 12. It's free, easy and (supposedly) very effective (every child learns in a matter of weeks). Children naturally do some kind of photoreading (no specific hand and eye movement, only fast page turning). If you're interested in the adress of tha web site let me know.
The main thing is to keep them interested. Don't force it, but play with them. Let them practice with books they are interested in, give them candy when they are trying (doesn't matter if they get it right or not)... It comes naturally.
