I've traveled to DW alone, with small family, extended family and this July just with my 7yo dd. I'm pretty comfortable with the area so the only concern I have is us getting tired of each other. We will definitely have naps, even if it means SHE naps and I rejuvenate in the tub.
We are staying off site for a week in a large condo (thought the space would be a mind saver for both of us - including our own TVs if need be) then moving to POFQ for 3 nights. We've stayed in several places before but the pool appealed to my daughter. I liked the idea of it being a small resort and not having to tire out her little legs when going to the food court in the morning for coffee. I've never stayed at POFQ and it's my goal to hit all of the resorts!
We have stayed at WL during the holidays and enjoyed it but we all prefer the GF for its Victorian splendor. (my dd's name is Victoria Rose - I love dressing her up and taking photos of her in the GF lobby). We also stayed at the Poly concierge and LOVED it. I would go with the Poly - it seems to fit a kid's idea of 'vacation' better I think.
We are doing the dolphin swim for her birthday in July (don't tell her it's a secret ... I keep telling her it's too expensive
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I'm also letting her choose a character meal - she is saying Chef Mickey's but we've never done the GF character dinner and she is asking questions about it. Disney is great about birthdays! Remember to stop at guest services in EACH park and get a birthday pin! Your daughter will receive special attention!
I'm going to try and go it at her pace. If you make any PS make sure you let them know it's your daughter's birthday. I took my mother for a biggie birthday and she LOVED how people in the parades wished her a happy birthday! She also stood in the center of the FOTLK arena and the crowd sang to her!
Don't count out Epcot during the holidays! If you time it right you might be able to sneak some seats for the Candlelight Processional, a truly moving experience. The tree light ceremony at Epcot is pretty nice too. You can do DW during the holiday season without ever repeating doing what you did during the summer vacation!
Enjoy!