part of me is screaming that they are too young to handle this information and that you should wait to tell them but then again your sons change in behavior is probably related to your trip to the er. he may not know that you went but he probably noticed the change in your behavior that necessitated the trip to change your meds and he is being extra nice not to stress you out. there is danger of him becoming a parentified child, stepping up to take care of you, thinking you cannot care for yourself. that is why he needs to know what is going on with you. so you can just let them know that mommy is sick, as much as I hate calling what we have an illness but it is what kids can understand, just make sure they understand it isn't a bad sick. and you take medicine to make it better. you can describe the symptoms you get when you get sick so sick doesn't scare them. let them know you will be all right and they don't need to worry about you. they need to know that your cycles aren't their fault and they don't have to take care of you. hope it goes well. take care.