Hi Victoria,
According to the
2016 Disney Deluxe Dining Plan brochure, Guests ages 3-9 must order from a children’s menu where available.
If your child is aged 10 or over and is therefore classed as an adult as far as your Disney Dining Plan meal entitlements are considered, it might be possible for them to order from the children's menu if they do not like any of the options available on the adult menu.
The official policy is that it is up to the discretion of the restaurant management as to whether or not a Guest can order from the children's menu.
In my experience, servers at each of the restaurants will do their very best to accommodate requests made by Guests and to ensure that they have an enjoyable experience whilst dining there.
If nothing on the adult menu appeals to your child at any restaurant, they will most likely be able to request something from the children's menu instead. In most cases, you will find that they will be given a larger portion than that which would normally be given to a child.
If you are really struggling, it is worth asking your server if it is possible for them to have something which is not on the menu but is fairly easy to make, like a sandwich or toastie for example. Whilst this can't be guaranteed you will find that Disney are very accommodating to children who are picky eaters.
Wishing you a magical holiday filled with memories which will last a lifetime!
Emma