Well, what part are you having trouble with? Your post is kind of general, really. All I can tell you is research to the max. Read not only lists of symptoms and general descriptions of Depression, read accounts written by people who've been there, done that, bought the ugly t-shirt.
Though if you want to do a little more showing regarding Depression, rather than the obvious tell along the lines of "Anna felt especially depressed today. As her children ran around her feet, she looked at her veins and contemplated opening them" try mentioning stuff like the dirty laundry and dishes piled all over the place because she doesn't have the energy to do them. You could also focus on her children. Obviously, if the mother's depressed, she's not going to be at her attentive best. Are her kids running around in nothing but soiled diapers? To what extent is she aware and paying attention to them? Are they just running around with very little supervision? It's also possible that she may develop feelings of anger towards them. One of the things people forget about Depression is how often anger and sadness intertwine with one another until it's hard to tell where one begins and the other begins. It's possible the mother could eventually come to blame the children for her issues. At the time she's doing this, she may know how deeply irrational her thoughts/behaviors are, but feels ashamed of them and afraid to tell anyone because what would her friends/relatives think if she wasn't the perfect, caring mother?
Again, I'm just throwing some ideas out there to get the creative juices flowing. I myself, have experienced Major Depression, but I admit I haven't had kids, so I can't provide any information on what it's like to be Depressed while struggling to raise small children. If anyone wants to fill in the gaps in my knowledge, feel free.