You only have 3 meals where the price is likely to vary, this makes the math easier to calculate (once you get all the data, which can be trickier). Head to AllEars.net to find the prices of the menus, use the lower numbers for the meal when calculating savings on the plan(s) (it's better to underestimate savings than over

).
From a gut reaction, with the huge increase in price for next year's DxDDP, you're going to want to use at least 90+% of your credits to come out ahead. If the trip is 5 nights, this means you get 15 credits per person, and I wouldn't recommend spending under 14. (Keep in mind, I haven't done any math on this part, just going with my gut). Right now, you're using 11 (9 for the 2 little ones). With that current schedule, I could not see recommending DxDDP at all.
The
DDP aspect, with the large amount of 2TS locations you have, it'll make it very close. A lot will depend on what meals your doing for some of those (e.g. Ohana, 1900 PF, CRT). The same math can be applied here as it is for DxDDP above. My gut, again, is telling me that it's too close to call and I'd err on the side of caution by going OOP rather than DDP. But, running the numbers here will be even more useful than above as it's likely pretty close.
Now, both of those are considering paying for the plans rather than falling under a free dining promotion. If there is a dining promotion for your dates, and you qualify, I'd look into that discount vs. any room-only discount (which is really a misnomer, as most room-only discounts can be applied to packages) and see where you're likely to save more. If staying at a value or moderate, with 5 people, again, the gut slants toward the dining plan promotion, especially with the itinerary that you've laid out.
Also, don't get caught up with a common misconception that just because a meal costs a high amount, that it's a good value on the DDP (at least, with the 2TS locations). Let's look at a CRT breakfast for example. The adult cost is ~$52 and the child will cost ~$33.50. Combined, 3 adults, 2 children, this would be ~$223. Wow, that's huge for breakfast huh? Breaking it down though, for the adults, you are getting ~$26 worth of value per credit. This number is actually less than the credit cost you to purchase (for 2013, it's along the lines of $33-35 per TS credit, if I remember correctly). As such, for the adults, they are actually losing money by using credits here and paying OOP elsewhere (well, theoretically, it depends on where else they are going of course). Basically, if any 2 single TS meals combined are going to cost more than a single 2TS meal, it'll be better to pay OOP for the 2TS, even if it's a higher total!
Note that the kids' credits here are a little different. For the kids, each credit is getting them ~$16.75 worth of value. This is almost the nightly cost of the kids' plan! From a purely numbers standpoint, you'd get the best value paying OOP for the adults at this meal, and DDP for the kids (not taking anything else into consideration, e.g. other meals).
Lastly, this is also your first time and you're going to want to see and do as much as possible. Dining at Disney can take anywhere from 60-90 minutes for the meal alone, not counting travel (each way) and wait time (after you check-in, before you are seated). Travel can take between 30-60 minutes, depending on where you're going to and where you're coming from. The wait times average around 20 minutes, but some can get longer ('Ohana and Crystal Palace are both notorious for this). I wouldn't suggest adding to your itinerary any more, which basically excludes the DxDDP for your case. If you fall under a free dining plan promotion, it may change the math a bit, as you can be much looser with the offerings since it's sizable discount on the overall plans (basically, spending ~$40 per night on food vs ~$100 per adult (Free DDP plus DxDDP upgrade, vs DxDDP base)).