Hi there, Megan!
I absolutely love your plan of having a nice, quiet dinner for 2 on your last night at Walt Disney World! It's wonderful that your mom will be joining you so she'll be able to hang out with the kiddos!
On all of the Disney Dining Plans, the child credits, whether table service or quick service, can only be used on the children's menus for kids ages 3-9. You wouldn't be able to use the child table service credits toward adult meals at any restaurants. What you could do is make a fun reservation for Grandma and the kids to go out for dinner on their own! That way, you'd be able to use up those last 2 child's table service credits.
If you and your husband do decide to eat dinner at
Jiko - The Cooking Place, you could use your two Table Service credits to pay for one of you and pay out-of-pocket for the other. This way, you'd still get to enjoy an absolutely fantastic meal together on your last night!
I sure hope that helps, Megan! Thanks for writing in and please feel free to ask any other questions you think of as you're planning the details of your magical vacation!
Have a Pixie Dusted day!
~Jackie