Yea. My neon tetra's even eat the babies. They try harder then the actual platies to get a free meal. I can only assume bigger tetra's would be even more fry hungry.
If you want to give the babies the best chance possible without sticking them in a breeder, get some floating plants (water lettuce, hornwort, etc) or even fake ones that'll float. I will caution you, hornwort is a MESSY plant but does *ok* with even low levels of light so that's good.
About the janitor fish... not sure which fish you're talking about but I have simaese algae eaters, otos, and cory cats and none of them pay any attention to my babies.