As much as children may ignore our repeated requests to sit up straight or clean their rooms, when parents are stressed, kids notice. Some children, those who tend toward anxiety may worry about their parents when they show signs of stress. These children may also blame themselves for the stress, or feel it is their job to make their parents feel better.
Yes, it is best for parents to manage their stress and not let it spill over into their family life, but that's not always possible. The next best thing is to explain, in child-appropriate ways, what's happening so kids don't worry. For example, say: "I have a lot of pressure at work right now, I'm sorry I've been less patient. I'm doing what I need to make things better at my job, but in the meantime, good teamwork at home will help everything go more smoothly."