Yeah! Our young cats (8 months & 10 months) will growl on occasion. They don't do it all the time though. I've noticed that it generally happens if it's a small piece of meat that they're working on and I try to move it or get too close to them, then they might
growl. WHen they're working on a package of pre-made frozen raw, they don't usually growl. They are not more aggressive when I give them raw.
I read in a cat behavior book that that's normal, the growling that is. I think left over from their days of hunting. Instinctual, I suppose!
P.S. Your kitties are SO CUTE