I was in the same situation, when he naps, he has curtain calls for just about anything, milk, pee, look outside etc. I am very strict and bring him back to his room, no conversation and I point to his bed. He climbs in on his own and covers himself up and it usually stops after the second time. He is 31 months and he naps on and off, on nap days he also wakes up early. I try to keep him up and put him to bed by 6:45ish and he usually is up by 6:30. I would either move his nap earlier or cut it short. I can't even let my lo nap 30min or he will be up all night.
HTH
Jan