I have not ever experienced kennel cough with any of my fur babies. I do apologize I cannot give you any insight on this.
Keep close contact w/ your vet if you feel you see no improvement. These little one's can get better fast or get worse fast also...Try not to worry yourself too much. I know that's easier said then done.
Continue to try all types of bland foods. Baby food (Gerber meat sticks), boiled chicken, chicken livers, rice, etc.
I hope your baby is better soon. Please keep us posted.