When you're struggling with food or battling your weight, it's easy to self-sabotage. With constant self-criticism, berating our bodies, and punishing ourselves for things we did/didn't do, we often become our own worst enemies. But the things we are telling ourselves (subconsciously or consciously) can do us more harm than good.
Talk to your daughters about how there is no virtue in striving for being a 0 in any realm of life. See if you can get your daughters to see this size as ludicrous. Use humor if you have to. Most importantly, let your daughters know that you are aware of these sizes and that they are unacceptable to you.