offer normal foods as well - i used to get tonsilitis all the time, and remember the GP saying if i could eat, i should, and mum was told to always offer a normal meal. if i didn't eat that, then to look at other options, but it was important to offer normal food so that i didn't get to the point i wouldn't eat normal food when the pain eased

if you're not getting much in, fluids are important and probably look at options like hydralite etc so they are at least absorbing the fluids etc.

soup that has been heated then cooled is good too. noodles/pasta that is soft etc

a lot of it is going to depend on what your own child wants i guess