Exploring lines: using hand drawn lines on rocks for play. Challenging pre-writers to distinguish between straight and curved lines to help build their understanding of shape and help establish correct letter and number formation later. Visit http://youclevermonkey.com for more.
Quantifying with stones - this is a really simple idea for counting. Make sure you have the exact number of stones, that way you have a control of error (this child will be able to do the activity themselves and know if they have made a mistake).