Generally heart as well as organs aren't introduced until about two months into feeding raw as they are very rich. How long has it been since you started feeding raw? How many meat sources have you feed?
That being said, since they are so young, they'll more than likely adjust to raw faster than an adult dog with years of kibble damage behind them. Even so, when you DO introduce these rich sources, you want it to be very very slowly, tiny pieces, about the size of your thumb nail at first, and gradually working your way up.
If introduced TOO early, you will probably see mushy, dark stools... but that's' as much harm as it can do. It certainly won't "hurt" your dogs at all.