I'd highly recommend the Marne la Valee forum on Trip Advisor. There was a post recently by one of the destination experts that gave comprehensive details on each of the DLP hotels, distance from the park, pros and cons etc & if you PM one of the experts, they'll reply quickly.
Myself and DD (now 10) have been twice and stayed at the Disneyland Hotel. It's the most expensive but worth it in my view. Fantastic location, right at the entrance to the park and it's very magical, especially for a little girl. There are lots of opportunities to interact with the characters in the hotel itself, food is good, staff are fantastic and it's just a nice experience. It's a tiring holiday, lots of walking, long queues and the location of the hotel means you can pop back quickly during the day for a rest and if you get up for extra magic hours (8 to 10am), you're right at the entrance and then you can walk back for breakfast.
I usually book directly with Disney on the phone and so then I only pay a month before we go. So if a better offer comes up in the meantime, I cancel and re-book.
I would recommend lunch with the Princesses at the Auberge de Cendrillon to celebrate both your birthdays. You'll feel 6 yourself because you get so enthralled by the magic! Or else the buffet dinner at Inventions restaurant in the Disneyland Hotel. Lots of character interaction as they come round all the tables and do photos etc. When we were there at Easter, someone had a birthday at the table beside us and the characters came with the cake and sang happy birthday etc.
If you book on the phone direct with Disney, they'll ask you if your trip is for a special occasion.
On both our trips, we went for 4 days, 3 nights but I wished we had longer so next time (new year) we're going for 5 days, 4 nights.
Check out the forum on TA and have a great time!