I've had similar issues with my DH and having done some reading up, we (DH and I) have concluded that he gets like this when suffering from stress/mild depression (take a look at the online depression diagnosis tools and encourage your DH to do the same).
It's important that you tell your DH when he is being like this, and also that he recognises when he's being like this and why (and ideally that he apologises for being like it). Then you can look at the triggers and rationalise it and/or take action.
By "take action" I mean find some outlets for his stress. It might be as simple as taking a half-day off work, having a lie-in at the weekend or you taking the kids out of the house for an hour or two, having a beer after work with a friend, or maybe he needs to go to the gym and pound the treadmill?
Also make sure you get some time out yourself and a couple of hours as a couple every now and again (once a month?). Easier said than done with small kids, I know.
But please don't just dismiss it as grumpiness (although it might be!). I have seen a male colleague with three small kids descend into full-blown depression and it started like this.
BTW, I once posted a thread like this about my DH and was told to a) leave him and b) he was having an affair. Utter nonsense! Just be prepared in case anyone does say this.