It's not the coordination or intelligence, it's the emotional maturity. When you deal with toddlers, you learn to watch literally every move they make, because they can go from happy and interested to raging and flinging in seconds.
I used to volunteer at a place where early afternoons were often slow, so I took knitting or crochet along. When the boss started expecting me to watch her toddler son some weeks while I was at the register, I took my project bag along, but left it in the cabinet in back if he was there. That stopped when I had to go to the bathroom one day.
His mother knew I was in the bathroom, but wasn't watching him because she decided to make a phone call. He unlatched the cabinet, climbed up the shelves and pulled my bag out. He ripped out the piece I was working on, broke the needles, got hold of the small scissors attached by a cord and cut the cord, then was trying to chop the strap off the bag when another worker noticed him with the strung-out yarn wound around his baby sister's neck and his own.
He was unattended for less than five minutes. No more yarn, string, scissors or anything else of mine went into that building.