Building blocks are great ways to develop a toddler's skill at stacking, but you can do other learning activities with them too.
First, you can separate a few blocks into groups by color. Give your toddler a block and ask him/her to put it in the matching pile by color.
To continue the grouping activity, ask them to find the matching letter of the block that you select.
When they are starting to identify numbers, you can use these same activities but with numbers.