the old fashioned remedy is to put a fine muslin or mosquito net over the baby's cot...the cat usually won't jump in because when they test the survace it gives too much. you could also set up the baby's cot and check on your cat, whether it jumps in or not, and freak it out with a loud whistle to discourage it being in there.

i shut my dog in the laundry at night, and my sister does with her cats, no exceptions. it's not too late to start training your cat.