Hi Bianca,
With any of the Disney Dining Plans, they are not a deal if you do not receive a benefit from them. I like to use the dining plan to dine at nicer restaurants as it is like have a preset price on my meal.
For your family, your two year old will not be able to have the dining plan because the little one is under the age of three. You will not even buy him or her a ticket. He or she will share a meal. For your four year old, you will pay about $12 a day for a meal as of February 2011. This is really reasonable at Disney World for a child.
I suggest you look at the
menus for the restaurants you would want to dine at while touring. Then add up the price of the meal. If you are over the price for the dining plan, go with the dining plan. If you are under, then pay as you go.
Wishing you a magical vacation!
Beth