- While its possible Rick decided it was in his families best interest to not tell them everyone is infected even though he knew that ; I think its more likely he did not tell them because he did not know. ( I find it hard to reconcile Rick suppressing that vital information, but also deciding its worth the risk to let his child possess his own fire arm )
This is pretty much my thinking too. Rick's whole deal this season has been his struggle with doing the right thing versus his need to protect his family and the group.
Now, telling everyone that they're all infected may destroy any hope the group had for something that resembles a normal future, but he would have weighed that against the danger of keeping them in the dark. What if someone dies while he's not around, and the group is oblivious to what's going to happen to that corpse? Suddenly they've got a walker slap bang in the middle of their safe haven. That puts his wife and kid in unnecessary danger, and I can't see Rick allowing that. It just doesn't fit with his character.