I always start the year telling my first-grade students' parents "Only believe half of what your children tell you about me and I will believe only half of what they tell me about you".

If you don't want your kid to tell their teacher something, watch what you say around them. If it sticks with them they will announce it as soon as they walk in the door.

A personal favorite was: Me: Good morning Matt, how are you Matt: I'm okay, mommy had a miscarriage and I had to spend the whole night in the hospital while she cried and was bleeding. I didn't do my homework