Ever notice the shape of the shoes we put on toddlers' feet? They have wide open toe boxes, with plenty of room for toes to splay out as they naturally would. They're flat too, so the toes aren't pushed up against the tips of the shoes.
The shoes we wear as adults are very different, however — they're often narrow, with pointed toe boxes and raised heels. These shoes put pressure on our feet and toes and change the shape of our feet over time. This is especially true for those of us with feet that don't conform to the average shape — wide feet, long toes, smaller arches, etc.