I have that problem in reverse. When I see the little hurt face (husband is diabetic) I just take mine aside and have a nice little chat. When my daughter badmouths her dad, though, I remind her that he's still her dad, that he's sick, and it's why I try to instill healthy eating habits so that SHE doesn't grow up to be sick, too. Then, we pray together for her daddy.
The cool thing here lately, is that her daddy and she have actually been bike-riding together, because she finally learned how! (She just turned eleven).
Hubby's getting some much-needed exercise, and has been in real good spirits this past week.