R., the flu shot has thimerosal, which is MERCURY, in it. Most infant vaccines do not contain thimerosal anymore but any doctor will tell you that the flu shot still has it.
Some kids have no reactions to shots, some kids do. You just don't know. My older daughter had bad reactions to vaccines and the flu shot and she was recently diagnosed with autism. My younger one never had reactions (we're now taking a break on vaccines until she's bigger and stronger) and so far, she's neurotypical. And I pray she stays that way!!! I would never knowingly allow her to be injected with mercury. Some kids are just genetically "stronger" than others.
So for the parents who's children never had reactions, good for you. But you can't speak for all kids. So I would recommend holding off, especially on the flu shot, WHICH CONTAINS MERCURY. If you ask your doctor about the flu shot, he or she will say "it's just a little mercury." Disgusting.