Historically, the minimum stay for a Free Dining Plan package has been 3 nights. (Even the current offer has a 3 night minimum stay, they just don't advertise it beyond the "Check for other package lengths" text). So, a 5 night stay should be covered.
Now, as far as early Feb, it's pretty likely, at least up until Mardi Gras/President's Day. After that period though, it's pretty unlikely as Winter/Spring Break season starts then and runs all the way past Easter. Do note that Mardi Gras is a week earlier than President's Day Week this year, so that may have some positive impact (well, for guests

) on crowds during that week and discounts are possible then.
In essence, we simply won't know for another couple months, but mid-late Jan into early-mid Feb is pretty likely.
As far as staying CL at WL with only 1 kid needing a plan, my gut is hinting that a room discount will likely be better. But, let's take a look...
A standard room at CL in early Feb (I looked at Sun Feb 03 - Sun Feb 09) is $455 weekday, $488 weekend. So, looking at a weekday night (since it's cheaper and thus the value of a room discount will be less), a 25% discount would save you about $114 per night. The free dining plan would save you about $56 per adult, and $17 for the 5 year old, or about $146 per night. (Note: the weekend rate at that time of the year, with a 25% savings, comes to ~$122 per night)
Taking tax into account (since lower room rates also mean lower tax on the room): We get a room rate of 387.04 per weekday with the discount, or $516.43 per night without the discount. A difference of ~$129.39
So, my gut was wrong! However, it's close enough to determine if a dining plan is the right option for you at this point. (~$16 and change per night).