You know when..

You know you have a kindergartner when you hear her say to her brother...

"Do you want the line to leave without you?"

You know when you have a boy when....

Walking back to the car takes twice as long or maybe even three times as long because he has to pick up and examine every single rock on the sidewalk.

or...

When he brings you a dead bird clenched in his fist and is SOO excited to show it to you.