Our 13 year old has discovered that 'the baby is sleeping' works on everyone
It started innocently. He asked us to keep our voices down because his sister was napping. Very considerate. This week he has used it to get out of a phone call with his uncle, to avoid emptying the dishwasher (apparently it's loud), and, tonight, to skip a conversation about his maths test. The baby was awake for that one. She was on my hip, watching him say it. It is working better than any excuse I tried at his age.