I don't think it matters. When you check in they confirm how many are in your party and ages of kids - so just correct it at the podium. Leave your ADR as-is for now.
So when i get to the resturant on the day do i print off the reservation info and show it them?
I always take a print out of all my confirmation numbers, but have never had to show it to anyone at check in. You just need to give the name and time of reservation. They will verify party size, I have never been asked to confirm the ages of my kids, but I guess it's always possible. As someone else already stated, just correct the age if they do ask. Enjoy your trip!