Knowing your child's age is important, because a 10-year old can understand things better than a 6-year old, so can catch up quickly. But it's not enough. I have to ask you his/her rating if s/he has played in tournaments, or how long has s/he learned. More important, I have to do an evaluation of him/her, to see his/her ability to handle chess games, his/her maturity, and etc. I offer the evaluation for free, so we could have a better picture of your child's ability before we put him/her into the correct step.
The youngest GM record is 12, and the youngest USCF national master record is 9. If a child works really hard, s/he could achieve very high. So next time if you sit across a child, pray for your game.