There are many many reasons I love having my four year old around.
Here's one for you... She's the friend you always wished you had as a teen, you know ladies, the one who would gently but totally honestly tell you if you were making a fool of yourself? I had those friends then, but sometimes I obviously still REALLY need one.
On the bus, she leant over and whispered something in a conspirital tone and a half-amused-half-horrified expression. I didn't catch it. "What was that, sweetie?" Still in a whisper, but with greater urgency and a bigger grin... "Mummy, you're showing your boobies!"
I buttoned my cardigan up promptly. And remembered why sometimes that kind of honesty is JUST what you need.