Okay, we are converts!  We bought baby's first pair of sunglasses (not this brand!) with the velcro strap that goes around the head .  It didn't matter how tightly you put them on, she would either yank them off or they would slide down around her neck.  Then she snapped them across the bridge like a jock snaps a pencil.  Those inferior glasses were just too brittle to withstand toddler hostilities.

The rubber these are made of is great. When she tries to put them on herself she sometimes ends up with the earpieces almost poking her in the eye, but the material is super flexible and relatively soft-no injuries. I've seen her do some incredibly brutal twisting and pulling and they just take the hits. These stay on surprisingly well now that she has figured out she looks awesome in them.  She gets lots of positive attention from passerby on these glasses, they really are pretty cool.  I think it is easier to teach you little one to leave them on if you yourself are a sunglasses wearer.  Monkey see, monkey do.

A few cons:  She has kind of a narrow noggin, and these are slightly too wide for her face at 18 months, but I guess there is room to grow into them.
I wish there were more color choices, orange, emerald green, maybe stars and stripes?  Flames?