How can I get my husband to be more patient with our kids (extremely long--sorry)?

To make a long story short, one year ago this month, I quit my job to be a stay at home mom, and my husband got back in the work force after being a stay at home dad for almost four years. Aside from when my older two kids (ages 7 and 5) are in school, I have them 24/7 (I also have a 16 month old whom I care for during the day). I'm the one who cooks, cleans, makes dinner, changes diapers, helps with homework, etc. (Not complaining--just stating the obvious that my husband really has no home responsibilities aside from occasionally taking out the trash, fixing little things that break, etc.) I don't know what the deal is with him, but it's like he can't have a decent conversation with our kids without snapping at them. For example, this morning they were getting ready for school and apparently weren't putting their shoes on fast enough for his liking (they were not running late) and he lost his patience and said, "Let's go let's go. Stop screwing around." (He wasn't yelling at them or screaming or anything--he's just EXTREMELY impatient over every. single. thing. they do. I tell him to get off their backs, and he tells me that they need to listen and obey. My argument is that if they were older and farting around, that's one thing, but they're so little and young, and they're not doing it to be obstinate. They play video games and if their volume gets above a certain level, he yells at them to be quiet. If they talk too much at dinner, he tells them to be quiet and eat. (Very rarely he yells--most of the time he gets a sour look on his face and grits his teeth and talks to them.) You'd think that being out of the house all day, he'd be a little happier to see them. Our kids aren't monsters--they're just normal little boys. (Well, as normal as can be expected--our 5 year old has ADHD and our 7 year old possibly has Aspergers Syndrom). I'm not a violent person by any stretch of the imagination, but when he gets like this, I just want to smack the **** out of him. What can I say/do to make him realize that he's being a complete ****** and to back the hell off? Our kids notice this and I see after he's been grumpy/upset/snappish with them, their little faces crumple. Our 5 year old was in counseling for his ADHD with a psychologist for a while, and the dr. told me very early on to ignore the little things. If our son walks into a room and kicks a toy (not out of meanness--just doing it for whatever reason) to let it go--it's not worth it. I can't seem to beat this into my husband's head that it's not worth it to CONSTANTLY harp on them about everything. Help.