Our first Disneyworld trip was in January and we used the Dining Plan (one sit-down meal, one counter service and one snack per day, per person.) We didn't have a car. It worked out really, really well for us and we would do it again. But here's some tips to consider:
1) The "big namer" sit-down restaurants (Cinderella's Castle, California Grill, etc.) require two credits per person. This worked out for us, because we didn't want a sit-down dining experience every single day and "stored" the credits for these bigger restaurants. Why didn't we want a sit-down meail every day? Because...
2) ...sit-down dinners (and character dining experiences) take up a LOT of time! Your 3 year old may prefer to experience the park/rides/characters over sitting in a restaurant. Sit down meals require you to stop what you are doing and get to your restaurant at the reservation time. Reservations are pretty much required for every sit-down restaurant.
3) Even with the dining plan, we still ate cereal and fruit in our room for breakfast. Once you get to the park, you'll want to GO! -- rather than using the time to search for food everyone wants.
4) My family are big eaters, but we still ended-up with tons of snack credits. One PP was right -- don't waste any credits! On our last night, we went to a Counter Service restaurant which also sold snacks and used our credits by buying breakfast and lunch items we could eat the next day at the airport.
5) The dining plan starts on the day you arrive - even if you don't have a ticket for any of the parks. We had a late afternoon flight and our plane was very late...we didn't get to our resort until after 10pm. Hence, we all had 1 sit-down meal, 1 counter meal and 1 snack that we really couldn't use. However, as mentioned above, I made sure we used all our credits by incorporating the restaurants that required 2 credits.
6) You can use your dining credits whenever you want. (i.e. If you want to use all of them on the first day, you can.)
7) In general, the dining plan with the sit-down meal is going to require a lot more planning. You'll need to pick the park you'll be at and get reservations at a restaurant in that park (because it seemed to take forever to get around. Plus, we didn't pay extra for the Park Hopper pass.)
I hope these tips help you make a decision. Some of this stuff seems really complicated, doesn't it?? Enjoy your trip to Disney!