Not sure where you are staying, but I am basing this on staying onsite because I have never stayed offsite...
Under 9 months, I would just nap in the stroller unless it is hot - but you can easily go nurse in the baby care center and have them sleep there. I love those places.
9-24 months - 100% go back to the resort. Those kids need a good solid 2 hour nap to make it thru the entire day. Otherwise you risk having to leave before fireworks etc... That is my and my kids fav time of the day.
2-3yrs - I would still probably go back but if your child can do a 10 hour park day with only a power nap in the stoller, then I guess not leave. My 2 year old would melt by 6-7pm even if she napped 45min in the stroller.
over 3yrs - it would probably depend on the day, weather, how much they slept etc....
Also, remember the parks are open different hours depending on the year. Obviously a mid day nap stinks when they close at 5 or 6pm. We purposely go when the parks stay open until at least 9pm. We go at rope drop, leave from 1-4pm and then close the parks (most of the time!) This way we are still getting 8-10 hours of park time but we are also getting time at the resort, swimming and relaxing.
We also always add a resort day in the middle. Go get a big breakfast, swim, do naps and then go to DTD in the late afternoon for some dinner, shopping and fun. I make sure the kids are asleep by 8pm that day. It really helps break it up. I can't even fathom going commando with young kids but that is just me. Isn't much of a vacation if you are so tired at the end end of your vacation.
