This qualitative study investigated young children's mathematical engagement in play with wooden unit blocks. Two boys, ages 6 and 7, were independently observed completing the task of filling outlined regions with the various sets of blocks. Three major mathematical actions were observed: categorizing geometric shapes, composing a larger shape with smaller shapes, and transforming shapes. Results indicated that young children's block play with designed tasks promoted mathematical actions, which may cement the foundation for advanced mathematics learning. (Contains 1 table and 4 figures.)