Hello Amy
you have had lots if good advice, maybe the Shake recipe would be good while his mouth is healing.
I dont know if you have seen it on the board elsewhere but just incase you have not.

1 tablespoon Carnation
1 tablespoon Ovaltine
1 Package carnation instant breakfast
1/2 cup whole milk
1/2 cup half n half
2 cups any flavour ice cream
around 1350 calories.

Blessings to you and your family.
Take care
Marica