No. The maximum number of meals you can order at one time at a TS restaurant using dining credits would be the 2 Adult and 1 Child since that is how many are on your dining plan. The second child's meal would have to be paid OOP.
Yes, this! You can order whatever you want, but as PP said, the max dining credits you'll be allowed to use are however many are in your party (2 adults, 1 child) - the extra meal will have to be paid for out of pocket.