Unfortunately people have learnt to accept that sunglasses break easily and that is just wrong. If they break it is usually because they have been incorrectly designed or made of inferior materials to reduce price and / or increase profits. You will notice that most sunglasses have no guarantee, the manufacturer knows they will break.
Some have a limited 12 months guarantee, so quality should be a little better.
Try looking for a full 3 year guarantee, that will not be easy to find and we only know of one company offering this, yes Idol Eyes.
Prices on good quality baby / toddler sunglasses should always be affordable.