Hi Lutfa,
If you want to visit the Theme Parks, your 2 year-old will be free. The rest of the kids qualify for a child ticket, which is less than the adult price. However, I agree, a one day ticket to the Parks for a family of 7 is quite expensive. When you buy multiple day tickets, the per day price goes down.
If don't have the funds to visit the Parks this time, but do want to dine with the Princesses then I have a suggestion for you. Two of the main character meals that have Princesses are located
inside of the Parks (so a ticket is required). However,
Cinderella's Happily Ever After Dinner at 1900 Park Fare is inside the Grand Floridian Resort & Spa (no theme park tickets required). Cinderella, Prince Charming, Lady Tremaine, Anastasia and Drizella are often there to welcome guests.
Since Advanced Dining Reservations can be made up to 180 days in advance, you'll want to call 407-WDW-DINE as soon as possible to see if you can get in.
Wishing you a wonderful visit to the Happiest Place on Earth,
Kaylene