To chicken out (spring chicken, spring lamb...)
Wise old owl (a night owl)
A piece of cake
Stand tall (tall order)
Child's play (a poster child)
To dawn on (the crack of dawn)
Horse around (from the horse's mouth) Animal idioms: Horse
Hold the fort (to be like Fort Knox)
Sour grapes (heard something through the grapevine)
Chew the fat
Turn the page
Bread and butter
Wash your hands