I believe it's because he thinks he is going to get into trouble if he tells me. I know I haven't balanced the whole telling the truth v discipline thing very well, erring on the side of discipline over cutting the kids some slack when they own up.
Me: 31, W: 29 T: 4 M: 2 Kids: 3 (SS: 7, SD: 4, D: 3) Separated, still living together: Nov 2013 Separate bedrooms: Feb 2014 W working away; kids with me: Nov 2014