When my reds were babies, their main diet was tropical flakes: they loved it!
It's not harmful for them: just make sure to feed them other stuff as well (brine shrimp, mosquito larvae, blood worms and other small food items).
So, don't worry about feeding flakes to your p's: sooner or later they'll stop eating it, but until then, just do it!
they are fine. but other things are much better for them. like shrimp,krill,bloodworm,beefheart,smelt, any type of frozen fish really. i wouldn't make their diet mostly flakes. wont grow as fast and the other stuff is better for them.