Apparently, if you have children under six years old, you have a legal right to request flexible working. Get yourself home a bit earlier, or perhaps (seeing as email, computers and technology makes things so portable these days -we generally work in cyber-space) see if you can work from home? Although, that may make things harder. Being a freelance journalist, i have to work in the shed just to get some quiet!
The other side of it, though -and I hate to sound like a woman- is that being at home with young kids is incredibly tough. The idealist viewpoint would say that it's all about daytime TV, playing with the children and pottering around the house before popping down to a sociable parent and toddler group. We all know it's not like that though! You've probably heard it from your wife (I know I hear it from mine every day) but she is at work too. Those kids and balancing the house duties and meal making -and just the NOISE dammit! It's very intense and doesn't let up! Consider why your wife wants to sit at the computer while your kids still have energy to run to the front door shouting 'DADDEEEE!' -those little critters just don't stop until you read them a story and put them in bed. Even then..
I'm aware I've sort of taken the female point of view, which may get me hanged -dunno what you're all like yet.
What it comes down to, though, is the perception that each of you have about each others day. She thinks you're in an office, sneaking in an internet browsing session, before getting another coffee and having 'just a chat' with the new receptionist -y'know, the one with the see-through blouse! And it may be true to say that you don't appreciate how intense her day may be if you think that YOU are the one that needs to unwind -up until you walk in the door, does she have any unwind time? It's fair to say she's been 'on the go' for as long as you have! What would she give for a quiet train or car ride.
Damn, you'd think my wife had hijacked my forum account, wouldn't you? It would seem I'm speaking as much to myself as I am to you...in fact that's very true.