So there are times when my children get water from the kitchen sink and use it on the flower boxes. I've noticed that some of the flowers look like they are dying. Do you think it could be from the salt in the water from the water softener?
Deffinitely. Most water softeners give you two kitchen faucets, one with treated water and one with raw water. The plants should get raw water, and you should also use the raw water for drinking and cooking.
A water softener is actually harmful to plants because it dries them out. It would be better to use tap water from a gardening hose since it may have more nutrients to support plant growth.