I have one required field but only when an option is choosed before. So, the problem is that you can add to the cart without complete this required field.
You can try:
– Color
– Cantidad
– Pecho (here you can try all except “sin estampaciĆ³n”)
– DON’T mark “Derechos de imagen”
– Add to the cart.
I checked your given product URL, the two cart quantity box is rendered on your product page and these are hidden. Duo to this your required functionality does not work properly.