Tomorrow, start with one yes
You need one food they already eat and, if you want, one new food beside it. That is the whole plan for the next meal.

The next meal is small
When you want the week written out, the shop list, and how to serve that food for their age, that is what the app is for.
Tomorrow morning you do not need a new philosophy. You need the food they already accept, on a plate, with you sitting down.
One new food, if the day is calm
Add it beside the yes, in a small amount. If the day is late or loud, skip it. The yes is enough.
Cheese and yogurt stay off that plate when milk is an allergy. The diet and the other allergies stay in force tomorrow too.
Then the app
The app takes the age, the familiar food, and the new food, and writes the seven dinners. It stays on the phone. It is $5 once.
This page will still be here tomorrow, with a different read. The plan itself stays in the app.
A sentence you can say
“Tomorrow we start with the food you already eat.”