I know that there's no exact science to figuring out how tall a person will be. I also know that there are laws of averages and mathematical equations can show you a lot.
Parent Center has a tool you can use starting when your children are two and going until they are twelve. I've always had fun typing in my kids info. Basically, you take their height and weight at certain milestones (every six months between two and twelve), plus Mom and Dad's mature heights and the child's gender. You type all that in to the calculator and then see how tall your child will likely be. It's also interesting (to me) to see how the predictions change with time. I have a spreadsheet for all of my kids medical visits (what for, why, who they saw, height, weight, etc). I just added a sheet for their height predictions. It's fun to see them side-by-side... How tall are your kiddos suppose to be?
Do you have the numbers from when your children (who are now grown) were little? Type them in and tell us how close the numbers are.