Why do my kneecaps get so cold when i am sitting down, could it be the two scars i have on each kneecap

Cold knees: Less blood flow. Consider scarring, peripheral vascular disease, arterial disease, rsd, or perhaps a sensory neuritis.

Possibly : When your knees are bent it causes a kink in the principal artery supplying them. It also puts the skin layer over the knees on stretch which decreases blood flow further. Add an old scar down the middle that decrease blood flow across the knee and you shut off much of the blood flow, especially to the lateral aspect of the joint. Try to extend them more and you'll see less of those symptoms.