Tea with Wendy would be perfect for a 4 and 6 year old. You will need to get the free tickets (time to get tickets will be in the navigator). On the 7 day, it happens at least twice, and they have been known to add a third based on demand.
Basically, Wendy appears and chooses 2 boys to be Michael and John. Then she has a discussion of a proper tea and manners and how this should be done. At your table, you will have hot chocolate and cookies, and will "take tea" with Wendy. It lasts about 1/2 hour, and is perfect for the ages of your DDs.