Hey Buzz!
I've never seen a line beyond one person (even in the old days at the old Barn) so it will be a fun event for the child.
I was at the Fort last month and took/posted two pix of the Pony rides. There is a counter/stall inside the public breezeway in the barn that looks like this:
Note the different prices for one "lap" versus "two" laps around the pony walk.
When I was there last month they had two ponies "working" that day but whether it's one or two, watching some other child enjoy the ride only heightens the anticipation.
Just outside the counter/door is the step up loading stands for the ponies (two only):
Basically the parent leads the pony by a rope as they complete one or two laps. The pony knows where he's going. The Cast Member will tell you the pony's name so you can talk to the child about the pony (my kids still remember Tonka the pony).
Go make some magic memories for the child and take plenty of pictures.
Bama Ed
PS - and come visit us on the DIS Camping Forum and say "hello".