J.C.
At those ages I would wait to take my shower until they are asleep or hubby is home. They are pretty young and you really cannot count on a 3.5 year old to understand babysitting even for a few minutes. So much can happen in just an instance, and you don't want to chance it. You are stressed out and I see your husband is not so good at helping out with the kids. NOT acceptable. You have a full time job too! You really need to talk to him and tell him what you need and when you need it for your sanity's sake. Lay it all out clearly of what he can do and when so that you get time you need. He is just as responsible as you for the children and the household. You deserve a break and he needs to step up and help.