Please help me! (20 chars?)?

6 months old is a crazy age for many cats and it can take a while for them to settle down. I would try buying some Feliway plugins and seeing if that helps calm Ninja a little, and clip his nails if you aren't doing that already. Another idea would be feeding him his favorite food when the baby is in the room (safely in your arms of course) so that he forms a positive ociation with the baby's presence. Really though, if he attacks her every chance he gets then he should not be given the chance. They need to be kept separate except when you are holding the baby or the baby is otherwise out of his reach.