Here's the link to the airport guide info page, with maps and all:
http://www.orlandoairports.net/guide.htm
For meeting up, do both you and the grandkids have cell phones? If you do, if I were you, I would tell them to pick up their baggage, then call me, and then go out to the street on the same level as the baggage claim and wait for pick up.
You, meanwhile, drive to the cell phone lot around the time you expect them to arrive. The lot is on the south access road for Orlando International Airport and it is fairly easy to follow signs to it. You don't have to pay to park there but you can't leave your car... it's just for people waiting for a call to pick up arriving passengers.
When they call you to say they're through the baggage claim, drive from the cell phone lot and follow signs to Arrivals - Terminal A. They will be waiting for you there.
If either side doesn't have phones, you'll need to park and go in to Terminal A. You could either go down to baggage claim and meet up by the carousel where their flight is unloading, or arrange a meet-up point using the maps from the website.
I remember the days of trying to meet someone in a big crowded airport before cell phones... ugh, hope you both have phones! In a pinch, they still can page people from a help/information desk if you miss each other in the crowds.