Hi Louise and welcome to the Mom's Panel!
Firstly, let me tell you that the Walt Disney World Food and Beverage Team is committed to offering a wide range of choices to accommodate Guests with food allergies or intolerances. Your desired dining requests will be addressed, but please note that in many cases, advance notice is required—usually at the time of your reservation, which can be up to 180 days in advance.
You can find out more about Special Dietary Requests
HERE
You do not state in your question the age of your toddler but just so that you know, Disney's Dining Plan is only available to purchase for Guests aged 3 years and over. If your Son is under the age of 3 years at the time of your visit, then I would absolutely make a note of his allergies when making your own dining reservations which will mean that he will be able to eat from your plate at no charge.
If your Son will be aged 3 years or above during your visit, then you will have to add the Dining Plan for all Guests in your party including him. In this scenario, you would need to make a note of his allergies against the childs meals when making your dining reservations.
I would suggest that you contact the Resort where you will be staying direct to find out if it is possible to request a kettle for making up special feeds for your child. Coffee makers can be found in all Moderate & Deluxe Resorts as well as Deluxe Villas but I have never seen a kettle available for use during any of our past trips. Cast Members at your Resort will be able to confirm if your request can be accommodated.
I hope that this information has helped and wish your family a magical holiday!