WDW doesn't care if you order children's meals and pay for them with an adult credit. What they don't want you doing is using credits that cost the children's price to order adult meals, or sharing the meals you get on the dining plan with anyone who didn't pay for the dining plan. So what they've done is begin enforcing that you may purchase only the number of meals in one transaction that you have people on your reservation. You should be able to order, in one transaction, a maximum of one child meal and four adult meals.
You could probably order the way you have set out, and get the requested meals. Child and adult credits are not separated at CS, and what they'd really care about is if you walk up to a CS and attempt to order 5 adult meals when you have 4 adults and 1 child on the reservation. The upshot might be that you've used one of the credits purchased by the adults to pay for the second children's meal.
You may have to keep an eye on the numbers of credits you have since the child and adult credits aren't separated.
There's also a rumor that Disney finally will separate child and adult CS credits in 2009, but we won't know if it's true until after 2009 starts.
