If you quietly explain to the waiter/manager there shouldn't be a problem.
1) Do not assume this to be true and valid at al locations.
2) If the kitchen at your selected eatery does not have alternatives, the manager can do little.
3) The chef might be able to concoct something for you, but not always.
4) As suggested, maybe you can buy something at a QS and take into the eatery with you.
. . . the eatery cannot warm anything for you due to safety precautions in the kitchen (except things like baby formula)
. . . so, the food might be cold by the time your child is ready to eat
5) The eatery manager WOULD allow you to bring in something from a QS.
NOTE: The only problem might be at a buffet or character meal.
. . . at each buffet, when you are there, you pay full price
. . . there is no price reduction for people who do not eat or eat very little
. . . yes, the manager can make an exception, but they rarely do
. . . so, you might pay full price for the kid and still need items from another eatery