Shar pei growls at family members

Please help. My 3 yo Shar Pei (Alf) has started o growl at my children (aged 18 & 20). Both children have always been in Alfs life, but about 2 months ago, my dog had a spinal cord decompression operation and he is paralised (at the moment). Because of his condition, both kids try to help me with his physio etc, but Alf will growl at them. Why has his attitude changed to the kids, its really upsetting all of us & kids dont want to help anymore.

I imagine he must be very distressed about the change in his health. Is he in pain? I would ask the vet to review his pain medication as the physio may be hurting which is causing him to growl?

He could be in pain or he could feel more irritable, and/or more vulnerable, if he cannot move.
Reduced movement also reduces his option to move away from something he doesn't like so he may feel he needs to get people to move away from him instead.
Nursing care and people behaving/interacting differently around them, due to the change in the dog's circumstances and health, including people being more protective of the dog, or concerned around it, can also influence how dogs perceive their relationships with various family members.
Could the dog also have associated anything about the spinal compression, its cause or associated pain prior to the operation, with your children?
Are you behaving differently with the children around the dog? E.g warning/reminding them to "Be careful of Alf"

Have you spoken to your vet about it?