>>Now for my question – If fatty food are so bad, why are my babies attracted to KFC?

I think that virtually all animals are attracted to high fat foods as an insurance to survival; birds and sunflower seeds, lizards and waxworms, humans and french fries. Fat is calorically dense and instinctively eating it whenever possible (it is of course much rarer in the natural environmentl) would help to insure survival and reproduction.
It's a holdover instinct that causes alot of problems for humans today however!