I don't know. I think that kids can be pretty oblivious. Especially if there is no obvious drama. Buying the story that "Mom wasn't happy" and then "Hey - Mom's got a boyfriend - glad she's happy" is easily done. After all - why would Mom lie?
On BD H52, W50 T27, M26 S21, D23 BD-9-Mar-16 D-15-Jan-18 Final-19-Apr-18 I am a storyteller. The story may do you no good. But a story is never for the listener. It is always for the one who tells