I made a big set of blocks for my firstborn out of #1 pine,
unfinished. The blocks outlasted the kid's interest in them (they
lasted many years before rain and drool caught up to them).

I thought of using maple, but then remembered that all toys become
weapons at some point, and decided to go with the softer species.

One thing I did that I recommend is to put a 1/8 roundover bit in a
router table and round over EVERY edge of every block. This goes
quickly in a router table.