Our first trip to Disney, our DD was 4 1/2 years old. We went back and forth about bringing a stroller, and in the end, we decided we would bring one. If for nothing else, it was awesome to have in the airport, but it was a Godsend in the parks. We brought a Jeep collapsable stroller, so it wasn't huge, but it did the trick. There was many times that she rode and napped. We also wiretied a cheap backpack on the arms of the stroller to hold a change of clothes for her, a washcloth, baby wipes (refreshing in the heat) and some other incidentals.
We stayed at the GF so that we could hop the monorail and go back mid day for a nap. That was key. We would go back for a few hours and head out. We also did the deluxe dining plan because we knew that we wanted to do as many character meals as possible. And while 3 meals a day sounds like alot of food, what it comes down to is this... you don't have to eat all of it.

For us, it was a great break to sit in the air conditioning and have some down time. There's alot at Disney and it's overwhelming for the little ones.
We also did
MNSSHP. At first we didn't know if we'd do it, would she stay awake long enough? But we decided to go ahead and do it. Well, that little girl pretty much closed the park!

We had her take about a 2 hour nap that afternoon, then headed back to MK at about 4:00. We ate dinner in the Castle and were ready to go. She had more fun that night at the Halloween party than I can even tell you. It is absolutely worth the price of admission, in my opinion. The rides are all walk on, you meet all kinds of characters, the Haunted Mansion is all dressed up in it's finest scariness...along w/ the CM's!!!
The best advice I can give you is take it slow. It's ALOT to take in. Use your stroller to keep them going and use midday for naptime.
I'll never regret doing deluxe dining... we did CRT twice and also did 3 of the 2 ts restaurants (LeCellier/ Flying Fish / Narcoosee's) On the days we did a 2TS meal, we skipped lunch and used snack credits for lunch. It worked out fantastic for us. My DH loved the deluxe plan so much that we're doing it again on the next trip.
We also did a couple of fun things for our DD to kind of 'pump up the pixie dust'. We got her a "first visit pin" when we checked in. We also brought 2 princess dresses with us, that she didn't know about. The first night, after she went to sleep, we layed the dresses out with a "glittered invitation" inviting her to Cinderella's castle for dinner. Can you just imagine the look on her face after we read her the ivite and she saw the dresses ?

Yeah, it was even better in person!! She thought Tinkerbell brought everything while she was asleep. It was a priceless moment that I'll never forget.
Also, when we were walking in the MK the first time, my DH went ahead of us in the tunnel.... he waited on the other end as we walked in....and he was taking a video to capture her reaction the first time she saw the castle.... well, it made me cry. She walked in, all tiny, and saw the castle and pointed and said "look, it's real, it's really real!!". Oh boy. But that was my sister's idea to do that and I'm forever thankful we have that on video.
Most of all, have fun. Take your cues from your child... if they get hot and sweaty...stop, grab a Mickey bar and relax. Most of all, have FUN!!!!!
